When I was young, while I was asleep or mostly asleep, I remember having this feeling overcome me like a trapping feeling like trapped in infinity and I remember screaming. What could this have been? It was a very bad feeling. I've also had OCD, although that would probably not be it. As a child I don't think I was stressed.
Thank you so much for trying to help me !

I think they may have been night terrors?

This explains what may have happened to you, and explains it far better than I ever could.

night terror: Definition from Answers.com

It is a very real, and sometimes horrifying experience for children. I am not surprised that you remember this so vividly.

Could be due to a tramatic experience you forgot or want to forget but don't. When you have these feelings try drinking some water. Yes, it sounds crazy but I have had similar experiences of hopelessness. I got closterphobia in the Army and feel like I can't breathe at times. I drink some water and sometimes take a ride in my car late at night or early in the morning when I get these same feelings of being trapped or unable to breathe.

Thanks. I haven't had a traumatic experience. But that only happened to me when I was younger, I think they were night terrors.