Sure, this is a medically proven condition in people with irregular/disturbed sleep patterns, like myself.
But that doesn't rule out that it has been related to paranormal activities. Something like this cannot technically be proven. That doesn't mean it doesn't exist in a paranormal sense to people who believe it to be true.
From my experiences, sleep paralysis has been hand in hand with my body resisting something called astral projection, which is very real if you have experienced such a thing yourself. These attacks may happen when you subconciously try to leave the body in REM sleep, the dream state.
This is why people often have visions/hear things if they think there is nothing paranormal about it. REM sleep is when these attacks normally occur.