if it is a demon, you should meditate and try to communicate. as you say, the spirit is there for a reason. it could be to help you, it could be lonely, or it could be taking some of your energy for itself. Rori [the spirit with me] he's been with me for so long we're friends, so i think it's mostly companionship why he stays, but also for my energy. he watches over me, and in exchange, i let him take some of my energy when he feels weak. speak with the spirit and ask what it wants.
you should also speak with your doctor to check if this tick isn't something medically wrong. i'm not trying to upset you, or say you're making this up, but when it comes to spirits, you need to cover all logical conclusions before resorting to the mystical. sometimes Rori will touch me, it'll feel like a cold hand on my shoulder or arm, sometimes he'll poke me in the side to make me jump, but normally things will move, or i'll hear/sense him. do other things tend to happen? try to list everything you think is associated with the spirit, then make a list of all logical conclusions, then see if they are correct. for instance, you suddenly feel hot, check to see if the temperature in the house has risen, if you've exerted yourself recently [i.e. running] or just drank a hot beverage.
like i said, try communicating with it, but be sure to also have a physical with your doctor to see if your symptoms aren't something medical. it's hard for me to describe how it is [communicating with spirits] but you should hear a voice [or feeling] as if someone's talking with you, not as though you're thinking the answers. the spirits i've spoken with all sound different, so i can't say what it'll sound like, but it won't sound like you, or your thoughts.