I totally understand.
I have a strange fear that one day I will wake up and the person I used to know as myself will be gone, and everything I identified as will never be seen again.
I know that most of the time what triggers these periods is a mystery, but I think that sometimes it occurs in situations where we are very conscious of how we are perceived. After all, our identities are to some extent sensitive to how we are seen by others. For me, in situations where the environment makes me feel very feminine (like when I'm around boys!) I suddenly lose my FtM identity. But I think I have an inherent, built-in male gender identity that eventually pushes through.
Oh well. Does this off-and-on cycle ever stop? I'm pre-op. Will transition influence anything?