What you wrote (your first post) may very well be describing an alter.
It sort of reminded me of how I perceive(-d) things and felt before I knew for certain that "I" was in actuality a "we", so to speak.
I agree with what the others have said.
It would do you good to contact your family doc and tell her/him about this.
Even if it would turn out that there's only a "you" (which I personally kinda doubt), it might provide you answers.
Like Viola told you, it is possible for alters to have disorders on their own.
One of my alters, Karen, has... I'm not sure of the clinical term, but it must be something severe since she's in a psych ward (actually it's a mental hospital, but I don't feel comfortable saying it) while the rest of us isn't.
"Anyway, I felt like I switched a few times yesterday....and it seems like there are actually 2 alters, and they struggled to take control and my body started jerking....I felt a pressure especially in my head and chest....and felt like going "back and forth" from places....then when I came back to take control of my body I felt surreal, I felt lost, as if someone pulled me from a leg and locked me up in a room and then set me free again...."
This, I have experienced more than one.
Like Viola also stated, it may be that you're co-conscious with some (or most) of your alters.
It's possible that you're the Host, and that's the reason you feel/experience that way.
So, even though it's scary, it's not unique. I.e, you're not alone.
Wish I could provide better opinions/thoughts than that, but sadly I can't.
'Though, I can wish you luck on your journey to "find yourselves".
// Sirpa & Co.