This has happened to me a few times now, i remember the last time it happened recently i didnt know wtf was happening, it took me a few minutes to realize what was goin on and i finally managed to get my toe to move.
but now i TRY to make this happen, seeing as you can experience lucid dreaming from this..
its super hard though, and i have not been successful yet.
although it has been a lot easier when you do some form of opiate.. i do remember when i smoked H all the time this shit would happen constantly.