Anyone out there experienced sleep paralysis?

Occasionally I suffer from a form of sleep paralysis, where I wake up and am aware that I'm in bed, but am unable to move.

In my head, I am trying to get my girlfriend's attention, to get her to nudge me awake, and I feel like I am trying to scream - but I can't move or make a sound.

Apparently, this is quite common though, and is caused by a "switch" in your brain that prevents your body moving as much when you are asleep (otherwise you'd be trying to run upstairs , jumping off buildings etc.. Every time you did so in a dream).

Sometimes, it takes a few seconds for that switch to turn back on again, connecting your brain's activity with the rest of your body.