Does anyone experience sleep paralysis?

I'm laying there, wide awake in my bed. I can see my surroundings, but I can't move. Then after what feels like forever, I start to hear things, and feel like I'm being watched. I try to shake myself awake, and when I think I'm successful, I end up falling back to that same state again. No matter how many time I try to wake myself up, I end up being in the same position again. I can even feel like the "thing" that's watching me is coming closer each time I try to wake myself up. It's scary, and after many attempts I finally wake up. I actually have to get out of my bed and walk around for a bit, to make sure I don't fall back into the sleep paralysis again. I notice this only happens when I'm laying on my back, or if I'm really tired or something.