Too Much Emotional Investment

I feel like I'm losing a little bit of sanity, here

or perhaps I'm losing myself into a reality that does not exist
investing so much in characters
that only exist in the mind

What does it mean, when you're reading something and suddenly your arm starts fluttering, jittering with...excitement?
Or when you can't control your emotions about a story, and your face and arms display a flurry of emotions?

Am I losing it....?

I think I might be.