Trouble sleeping, have you ever had this happen as you were about to fall asleep?

I've been having a really hard time getting to sleep lately. I'll be tired, and I'll start to feel fuzzy and sleepy - you know, that sort of not-really-with-it state you get in with your eyes closed, right before you actually fall asleep. Suddenly, I'll "jerk" awake and feel dizzy and disorientated, as if I am about to faint. Have you ever experienced this? I sometimes spend all night up, because I am afraid I'll stop breathing if I fall asleep...I know this sounds crazy, but it's really bothering me. (Also, if it makes a difference, I have dust/pollen allergies, and I am usually very congested when I go to bed).