"He literally shut completely down, and for a about 5 minutes just sat there with his eyes closed, breathing. I tried getting his attention, but he was complete

"He literally shut completely down, and for a about 5 minutes just sat there with his eyes closed, breathing. I tried getting his attention, but he was completely catatonic." When I was much younger (middle school) I had a friend who did this. I always wondered about this particular behavior. Anybody here know anything about why this happens?