Stage 4 Sleep

When I have a lot of work to do for school, I stay up late into the night to finish it and I sometimes I hear voices coming from other rooms in the house and I say to myself, "He must be in stage 4 sleep right now." This is the stage, in my opinion, that is the most interesting because it is the stage where people sleep walk and sleep talk.
My brother once slept walk into the shower and then took a shower, went downstairs and watched a movie, and did not remember any of it the next day. Gabe shared the story that his dad sleep eats sometimes, and I wish I was able to do that because that just seems boss. Anyways, from all of these great examples you can see how interesting this stage of sleep is but I also have a couple of questions about it:
1. How can you move around (talk and eat) without remembering it the next morning?
2. Why do these things take place in this stage?

P.S. I am sleep writing this so I must be in stage 4 sleep right now but I probably will not remember this tomorrow.