To start, I am going to talk (Err... write?) a little about my own experience and learning regarding the phenomenon and community. I have been a part of a couple of vampiric communities between 2001 and 2015, with the last couple years being more or less an off-and-on visit. Most notable of the communities was Sanguinarius.org, and primarily their MIRC channel on Dal-net. (yeah, I'm old. I know what IRC is.) And at about this point it might behoove me to mention that no, I am not a vampire/vampiric. Instead, I used the community as an opportunity to practice at being an energy worker and channel by being what the community refers to as a Psi-donor. I'll get into that in more detail later. For now, suffice it to say that I channeled energy for those who needed it.
Which brings me to what vampirics are, and what they are not. To do that I am going to start by separating history and fantasy from modern expressions/recognition. In history, there are several real figures who were labeled as vampire (among other things) and they were people who were typically in places of power, and who had a propensity for violent action, gruesome display, and acts of cannibalism in a variety of forms. Among them are Emperor/Caesar Caligula of Rome, Vlad Drakul the impaler, and Bloody Mary. While they have been labeled with such supernatural titles like being vampires (or at least compared to them or associated with them), it is a label given to people as a result of their actions. Other 'vampires' are usually described as people who have been possessed by a demon or other evil entity and so driven to inhuman acts.
In folktale and lore, vampires typically begin with a single person who was once human but then becomes cursed for one reason or another. Examples include Ambrosio being cursed by Apollo, the children of Lilith in biblical writing, Vetalas and so-on. Among them there are a few common threads as to what defines something as vampiric. An aversion to sunlight- often with sunlight causing harm, a predatory nature, being long lived and difficult to kill, and having a need or craving for human blood, or otherwise a requirement of subsisting on humans.
When vampires started appearing in fiction and later in media, these traits have been stretched and changed to suit the story, or to try and place a unique spin on the idea and concept to excite attract an audience. To this end, the concepts and origins and abilities associated with them have gained a very broad range. The modern representation also involves more of a heroic or anti-hero attitude. Often they are portrayed as the 'fierce warrior with the heart of gold'. Or as the love interest with a dark past, or similar modern story tropes that have risen to a great deal of appeal and had influence on several groups such as the Gothic and Emo counter-cultures, who have been known to actively emulate these perceived ideals of darkness, separation, misunderstanding, and the 'noble martyr'.
In today's understanding of vampirism, those of the vampiric community recognize it as a spiritually based condition. So other than in perspective of whimsy or willful emulation, neither of the perspectives already mentioned are relevant or applicable directly to the phenomenon as it is currently understood. This translates to a perspective that sets aside several ideas that are seen to be untrue in relation to currently living people. To that end, people who identify themselves as vampires (usually calling themselves 'true' vampires) are not long-lived or immortal. They are not negatively affected by sunlight, garlic, holy symbols, silver, etc- barring allergy or over-exposure like most normal humans. They also are not 'created' or 'turned' into vampires by being bitten by another vampire, nor through magic ritual, spell, or pact. Ideas of supernatural tendencies are also routinely dismissed, like being stronger or faster than others, having superior sight, hearing, or other senses, being predisposed to nocturnal lifestyles, etc. And most times physical 'symptoms' like allergies and sensitivities are recognized as either coincidental, or psychosomatic.
So, after all that time spent in establishing what they are not about, what is it that -does- lead one to defining him/her-self as vampiric? How does it work and where does it come from? It is the one common thread that is left of the bunch; The dependence on gaining some form of nourishment by taking it from other people. However even that, too, is not quite what the mainstream expects.
Within the community, vampires refer to themselves in one of two ways, either as a Sanguinarian, or as a Psionic. Usually the term is truncated to sang or psi, respectively. Either way they are unable to easily maintain a healthy level of energy on a spiritual level. Vampirics have difficulties in drawing that energy from normal sources like through rest or meditation. This can lead to a certain lack of emotional wherewithal and so they tend to feel emotionally drained very easily. This leaves them more prone to stress, anxiety, and depression.
It is not uncommon for healers and other energy sensitives to notice a weaker or muted aura, where the energy of their system tends to be almost sluggish and described as 'leaking'. While this isn't necessarily an immediate health concern, it is not uncommon for vampirics to complain of weakened immunity, lethargy, anxieties, and various forms of depression that can have more long-term consequences. Usually the longer the period between opportunities to feed, the more acute the 'symptoms'. Because of this, vampirics need some sort of intermediary or bridge that can draw this energy closer, making it easier to connect with and draw from. IE; other, normal people who have a healthy method of making, accessing, and/or holding a healthy level of energy.
For a Psi, this can be accomplished a few different ways. Gatherings like parties, concerts, sports games, or anything else that can develop a crowd with an emotionally charged atmosphere can be a ready source for some. However it is difficult to manage what kinds of energy are drawn in. It is sort of analogous to sticking a straw into a puddle and hoping the water you get isn't dirty. Other times it is done with smaller groups or individuals, and of course during acts of intimacy or other deep connection with a partner or spouse. Most often this is a consciously directed act through developed sensitivity to energy, visualization, and meditation. However for some this also can sometimes be an unconscious act and so less controlled or purposeful.
For all sense of practicality, Sanguinarians have a need for this energy as well. The exception is that they require a much deeper connection with a source of energy to be able to connect with it and draw what they need. In magic, blood is the ultimate personal connection for placing energy and your very essence into a magical working. Blood is symbolic of life, and is of course tied to bloodlines and genetics. So blood is both literally and figuratively the essence of who you are. It is this premise that allows a sanguinarian to use blood to connect with and draw the energy they need. This also means that very little actual blood is taken in as it is more about the awareness and connection formed through it. In the end it is about getting this highly intimate level of connection directly to a specific person that allows them to gain access to energy.
Of course the ongoing question lies in how and why this happens. What is it that makes a person become dependent on taking energy from others, why can't vampirics obtain or maintain their own? School is still out on the subject, with a few different themes running the circuit. Truth be told however, like with many things there is no one cause or defining factor. I find it to be a more individual affliction that has many ways of coming about, with different people encountering the issue for different combinations of reasons.
On the Psychological front there can be an underlying need for recognition and emotional support and I have a habit of comparing this aspect to versions of co-dependence and depression. In this, there is some sort of personal dependence on outside support for coping mechanisms or feelings of worth/self-value. It usually manifests as a need for others to provide moral support, and to give care and attention and concern to assure them of any negative life encounters they have. Basically, there develops a dependency on receiving external sympathy or acts of caring as a means of venting internal stress and negative emotion.
When looked at through a more energy-focused perspective, it can be perceived as one (or a combination) of two things. There is some reason that as a person, a vampiric is unable to 'hold on' to one's energy and so it is constantly out of balance within the body as chakras and other energy centers are shifting high and low, open and closed, and otherwise having energy run away from your center, or by the individual constantly 'giving away' their energy at a rate faster than the body can maintain. Or, the body is for some reason unable to connect with the Higher self, or other sources of energy in a natural or automatic way. In essence the person is 'unplugged' from the sources of energy around them and so even though their internal energy system is by and large balanced and clear-flowing, it just can't recharge itself.
On a larger spiritual scale, the situation gets looked at from an angle involving past lives, and/or life between lives. Primarily the theory lies in some sort of past life event or trauma that leaves a lasting impression on the being of the individual that is strong enough to carry on to future incarnations/lives. Think of it as the spiritual version of a bad scar that has changed the natural flow of the person's energy. A deep-set emotional (and sometimes physical) mark on the soul that has been unable to be healed or let go of for any of a variety of reasons. This theory ties in with ideas of cellular memory, karmic chains/cycles, and similar ideas that past life events can carry over to present incarnations in a number of ways. Usually, the things a person experiences and learns from, both good and bad, become more subtle notes of a person's personality. But somethings they can surface in more direct ways. One of which would be a sort of partial dis-connection between the self and the higher Self, or inabilities to balance or move or connect to personal energy, or having particular energy centers be more sensitive to imbalance or otherwise twisted or less functional.
Like with most things, personally I take a Wholistic approach to the situation, and so I tend to see how all three ideas have merit. I consider that each aspect overlaps and influences the others, and the only real question is in which factor is most prominent. For that, all I can suggest is that it is different for each individual.
So just to round this all out and conclude the discussion; To answer, finally, the initial questions often asked;
Do vampires exist? By way of literary description, no. The closest equivalent would be some form of malicious haunting entity. However there are people with vampiric tendencies who have a need to feed from other humans, and so adopted that monicor.
Does being a vampire give you 'powers'? No. Absolutely no. if one is a vampiric, the most one can expect is to maybe have a predisposition towards energy and emotional sensitivity. Though like anything else it is up to the individual to nurture that predisposition to make anything of it.
Can a person be turned into a vampire? Again, by way of the literature, no. But it can be developed through psychological process. Or severe trauma that affects a person on so fundamental a level as to cause long-lasting harm to a person on an energetic or soul level. It is not a voluntary act so much as a consequence.
Can a person who is Vampiric, heal the cause or otherwise move beyond the affliction? Yes. However it is difficult as it requires some form of personal and fundamental psychological or spiritual growth and healing.