Possibly Sleep Walking

Sleep walking is fairly common for kids and most out grow it.
Don't let him outside.
Direct him back to bed and tell him it's cold and he'll cool down soon.

http://kidshealth.org/parent/growth/sleep/sleepwalking.html

I don't sleep walk but I talk in my sleep.
One time I pointed at the window and said "They're coming. The seals. They're following the wire.".
When I was young and in chorus at school my Mom would hear me singing in my sleep.
My husband thinks it's pretty funny - we've had some interesting conversations in the night that I have no memory of - he tells me about them next day.

Yes, I believe it is. My 11 yr old daughter has done this from time to time, but not on a regular basis. She usually doesn't make sense when she talks, and that is my first indication that she's sleepwalking.

You should not let your son go outside unless you're right there with him. He could wander off without knowing where he's going, since he's not really awake. When he does it, give him a cold washcloth for his head to cool him off and lead him back to his bed.

Has he ever had any surgeries that he's been under anesthesia? The reason I ask is that my little brother used to do this, not sure if he still does, he lives w/his g/f now. But he had a surgery & had anesthesia for an extended period & his dr explained to my parents that oftentimes this can be a long term side effect. If not, the most important thing is really not to wake him and to just be sure all of the doors have locks high enough so he can't get out. I would speak w/your pediatrician about it. Best of luck to you.

A form of night terrors. Have him go to bed a little earlier or a bit laager. Need to break the cycle. That's what I had to do. Changed bedtime and problem went away. Good luck. My son used to run around screaming. I physically had to restrain him. Scarey for you, they will not remember the whole thing.

I did that a lot when I was his age.

I have read on here several moms who said to wake him up just before you go bed yourselves, so that his sleep cycle is disrupted. (It doesn't take much.) They have said that it stops their kids from having night terrors, which what your son is doing sounds like.

Try that and see if it works.

My step daughter sleep walks. She is 10.5 and has done it as long as I've known her, over 5 years. It usually happens about an hour after she goes to bed. She sometimes cries when she sleep walks. We've caught her getting in the shower (clothed), going into her sisters room and turning on the lights, as well as other parts of the house. I do worry one day she might try to go outside when we are sleeping, but so far it only happens when we are still awake so my husband will quickly steer her back to bed. My 4 year old often wakes up an hour or two after falling asleep and is very disoriented and not able to console. Then suddenly she just crashes back to sleep like it never happened. Anyway, I think it's fairly common.

Around age 12, I would shower and dry my hair while sleepwalking. My mom would just steer me back to bed.

My daughters sleep walk every once in a while. We just tell them to go back to bed and they do.

Do not let him go outside. Do not try to wake him up. Steer him back to bed. Hopefully, he'll grow out of it soon.