Why are some people walk in their sleep?

We cant say the reason because we are not Dr. but Dr. can say the reason of this and the person who are walking in sleep they also not know about this. When they wake up they not remember they were walking in sleep.

You can't stop your friend from sleep walking. I have been sleep walking for years. One night I woke up about a half mile from my home carrying a baseball bat, barefooted and wearing nothing but a t-shirt. I was coming out of the woods. When I was 8 years old I almost got shot by my father because he thought I was a burglar. I had been sleep walking and was trying to climb in the bedroom window. I was muddy all over, barefooted and wearing nothing but a gown. I woke up many times, when I was a child, with muddy feet and my mom would have to change the bed sheets. One night in 2005, I had lay down on the couch to watch t.v. I lay my cell phone on the table by the couch, my cars was beside it. I locked the door and went to sleep. What is important to this story is where my car was parked. There was two trees in my front yard about twenty feet from my porch. I had parked my car between the trees and my porch. There was also 3/4 tank of gas in my car. I woke up at around 4:30 a.m. My front door was about 1/2 open, my phone nor keys was on the end table, they were on the counter, the t.v. was on a different station and my car was parked by the side of the house. I went outside to my car and found my purse in the seat. I checked the mileage and the gas and there had been 80+ miles put on the car and I only had 1/4 tank of gas in the car. I was perplexed. I don't couldn't figure out how this happened. I lived alone so no-one else could have taken the car. I was told that I drove it in my sleep. Sleep walking can be dangerous. There was a woman on inside edition that said she went sleep walking and woke up in the river or a lake. My parents used to put locks on the doors to keep me inside. After I drove my car, my son came to stay with me and would hide my keys. I haven't been sleep walking in several years now. I think stress has a lot to do with a person sleep walking or something is bothering them. I don't know. If it happens a lot with your friend you may want to get him help.