Tt just your sub-conscious mind. Think it has sth to du with REM
or sth li tt.
Go watch the navy seals hellweek video on youtube. When they were
allowed the chance to sleep, many of the seal cadets' legs and hand
were jerking away. The instructor explains it that their active
minds still believed the body was in the training mode. Anyway it
happened to me so many times, its quite common. Tt time in the car,
I woke up with a jerk and banged my head against the window.
As for the TS's question, yes, I am positively sure its sleep
paralysis. No biggie, happened to me before too. At first I thot it
was SARs, cause it first happened during the SARs period.
Haha.
Normally, the breathlessness or the pressing feeling will wear off
before you wake up really gasping for air like a drowning person.
Tt was my case, so I didnt really care much. But still, the feeling
of the inability to expand your chest when you wake up can still be
quite shocking.
Go read it up in wikipedia.