Technically, we aren't supposed to know what ours is until we're dying, but being magicians I guess we find ourselves in liminal spaces often enough to maybe catch sight of it and survive.
To my understanding, tradition had it that everybody was accompanied by a Fylgja, which meant "a follower" and was related to the word referring to "placenta/afterbirth". This expresses, I think, a more accurate term for an animal spirit guide than either totem or familiar , both of which refer sort of to the tribe or family. The Fylgja would be very individual.
I also used to know the difference between the Fylgja, the Hamr, and the Hugr, and how they were expressed with having to do with spellcasting or the mental/emotional forces behind any intention.
It used to be an old way of thinking that to see your fylgja was a bad omen, and meant death. However, a lot of modern practice actually involved working with the fylgja and using it in projection- much like an animal guide, I assume.
Familiars aren't really family based (or inherently animals), but are specific to a Witch in that a spirit would work with or for them (depending on the view).
I have not identified any of the spirits I work with as my fylgja, though my 'mirror self' reminds me more of the hamingja. When I say that, I mean I have visions that are actually of me either opposite standing or literally mirrored in looks. This other self is present most when I am outside (in 'her space' as it feels like) or in dreams involved with shadow self working. In these dreams, she is both me, and not me. This is why I've had difficulty identifying her as an aspect of myself or a spirit that simply takes on my physical form. Regardless of her identification, she is a spirit that I work closely with in a similar manner as mentioned above.
Were you looking for discussion to help find yours or were you simply curious of others'?
I've done workings with my own fylgja for some of the more shamanistic practices I do. I mainly use it when doing projection-related work. Meditating on my fylgja and its meaning is part of how I come to a better understanding about myself and what I'm doing. Your fylgja best represents you, and can actually change depending on how you change as a person. From this, you can gain a lot of insight into how you as a person are growing within your practice. Learning lessons from the various fylgja you may have can teach you a lot of different skill-sets that may be important down the road for you.