Ping out from standing up?

So like sometimes if I am sitting down and take in a deep breath and hold it then stand up I get REAL EFFED up. One time I did it in on the wrestling mat while the coach was making a speach and I fell down and ped out then woke up and it felt like i'd been asleep for 2 hours and everyone was looking at me ...LOL.... then i did it in a locker room fell down and bounced my head off the wall and got a concussion :( which consequently forced me to miss my last wrestling tournament. but anyways is this normal and why does it happen?