yes sometimes i get this. my treatment providers say it is normal for this to happen with things like sleep deprivation, medication over dosage and stress. with me besides those three things it also happens as part of my having MS (a physical health problem) and sometimes when I do my meditations...

short version it is a situation where a the brain prepares for sleep. it produces a chemical (Gaba) that is like a paralyzing agent. it makes it so that the body doesnt move when in REM sleep. the brain also tells the body to produce chemicals like melatonin. when its time to wake up the brain tells the body to slow down the production of GABA melatonin and other sleep chemicals.

in some people like me the process of decreasing levels of the chemicals in the body takes a slight amount of time where after sleeping instead of being wide awake right away I am in whats called Hypnagogia (in laymans terms this is being half awake half asleep) under normal circumstances I just lay there and enjoy the restful calmness of it. but sometimes on rare occasions my mind wakes up before my body does, where I know Im awake but I cant move, or causes me to have hallucinations where I will hear noises in my head like a huge bang or roar and physical sensations.

my treatment providers have me on some medication that helps with this. they are anti psychotics that control the production of the chemicals and rate that the receptors doing their jobs.

my suggestion if this continues to bother you contact your treatment providers. they can help you find the right medication for you.