I suffer from the same problem as you, it's called sleep paralysis. Basically, when you're in the deepest part of sleep your mind is not "wired in" to your body. When some people rouse suddenly from this sleep, they can be fully awake and aware but unable to move. For me, this often occurs after a vivid nightmare or night terror (a nightmare which continues after you've awakened).

For example: a few nights ago I had a vivid dream where I kept waking up in my bed, wandering around the house experiencing terrifying events, then would "wake up" in my bed all of a sudden, thinking I was awake (but was actually still dreaming). Finally, I actually awakened and looked around the room, saw the time on the clock and what was on TV, then had the horrifying experience of feeling a cold, pure evil entity in my room. It floated across the room to me -- I could not see it -- and plunged into my chest, causing me to act as if shocked by electricity. I could not scream, and only groans could escape my throat. I then saw an alien in my room making a waving motion towards me. After about a minute and a half, I finally snapped out of it and actually woke. I was quite shaken.

The good news: this is not uncommon, it is not medically threatening, and -- unless you believe in paranormal things like alien abductions, ghosts, or demons -- it is nothing threatening to your safety or health.

The bad news: people who experience sleep paralysis, waking dreams, and/or night terrors can suffer from Post Traumatic Stress Disorder (PTSD), the same affliction which plagues some Vietnam veterans which can cause depression, anxiety, insomnia, flashbacks, and even the inability to live among society normally.

It's important to keep the line between fantasy and reality straight. I'm not trying to debunk ideas such as abductions, ghosts or demons, which I neither believe nor disbelieve, but becoming fixated on this as something real only makes it worse, trust me. If it gets to the point where it's no longer a distraction but a serious hamper on your life, I would recommend seeking the help of a doctor or a sleep specialist.

-- Hope this helps.