What causes sleep talking and walking?

[Kris]

I am a 15 year old male and i have no idea why but i always talk in my sleep and according to friends and family it all varies on what i am talking about and where i go when i sleep walk. I don't know why because i never dream (well i don't know i am) and i go into a very deep sleep where the only thing that can wake me up is my stereo that is really loud. And i am not stressed over anything, I don't do anything, and frankly nothing ever happens in my life, I also don't think i have any diseases? Please help I'm curious and what all can i do in my sleep. I just saw the last exorcism and I do NOT want to kill anyone or anything in my sleep lol and i don't believe in god or demons or ghosts it just freaked me out lol so please help