Is This Sleep Paralysis? Help!?

Okay so this might be a little unbeleivable for some, but it's not the first time its happened to me. Last night in bed I must have been dozing off and slightly dreaming, and suddenly I couldn't move atall, I felt as though someone was grabbing me from behind and as if something was on my bed I could literally hear the covers... I tried to shout out who is that and "help me", and move away but it was physically impossible, my scream sounded ridiculous!! after about 10 seconds everything disappeared... is this sleep paralysis? or am I just going mentally insane. Help!?!?