I've had this plenty of times .. It's normal it's wierd but it's normal does you're heart beat fast once you have waken ?
I have had this on occasion in the past, but now that my anxiety is acting up again, I have a few times since. When it first happened it scared the living crap out of me, and still does, but once I am finally able to move, and fully wake myself I am not so scared as I used to be. Upon googling the sensation I came across this animated video that does a good job of explaining the phenomenon. Though as the video suggests, I have never hallucinated or thought something was sitting on my chest, though I did wake up in a panic state. https://www.youtube.com/watch?v=Ub8Wj_tJhdQ
Another thing that happens to me, is just as I am falling asleep, it sometimes feels as if a jolt of adrenaline surges through my body, and just before that happens, I get this feeling it is if I am loosing consciousness or as if "I am about to die" - at least that what my brain says, then I am jolted awake with that rush of adrenaline. I also hear that this is a normal symptom of anxiety as well.
For me, it seems to happen more when I over indulge in a little too much to drink the night before. It *****, I know, sorry you are going through this, I hope you find some relief soon.
I never really thought about my heart rate when it happens. I'm just relieved that I'm awake. I'll watch for it next time though.
I have had another add on to this just last night. I was dreaming and I got that same "aware" feeling and I thought I woke up, because I opened my eyes. A few feet from my bed I thought I saw a figure, but I could barely make it out. I was trying to focus on it when I just started shaking and fainting. Then once I fainted I actually woke up.
@imokyourok That feeling you get when your about to fall asleep and suddenly feel like you're losing consciousness could be a hypnogogic jerk. It's explained in a video on you tube. Search for Vsauce deja vu. They also have a video called why we dream, which is very interesting.