When a child faints or passes out -- what could be the cause?

My daughter is actually 12 too. She has passed out many times in her life because of dehydration. 2 on the ballfield (She actually passed out today just about half an hour ago) 1 at swim practice, 1 when she was sick and did a play. Another time at home when I straightened her hair. Her dad has the same problem too, so I guess it can just be in the genes? We've done tests on both of them, but the doctors find nothing. Its weird because every time she passes out she says her stomach hurts, is that normal? Make sure your daughter drinks plenty of water, and when she's badly sick try to make her move slowly, sometimes when people move too fast it can make them lightheaded.

I pass out all the time from age 1 to 5. I found out that all I eat was sugar and rice. Everything I eat has excessive amount of sugar. I don't eat vegetables or meat. Just rice water with sugar and sugar and rice. It helps if your child have proper nutrient in his/her diet.

I'm about to be 13 I think I fainted to because I was light headed because I stood up really fast and I was really light headed and I I guess I fainted didn't know how didn't know what was going on

i am 13 years old and i was just walking and thinking of what to do nest, now i found myself on the bathroom floor wailing and thought this was a dream i recollected being a bit dizzy and now i punched back to reality. it was neither a blackout nor a fain.
What was it?

i dont think kids need to do gym because once when i was a kid i passed out for over heating an that was the day when we had gym for the whole day

I'm 13 and I have felt really tired for the past 3 days and I don't know why I fell like I'm going to pass out a lot and I think I've had a few blackouts please help me!

My child if 8yrs 10months. He got fainted thrice in last one year. All 3 times due to excessive scolding.
I did consulted Child Nuro Specialist and he just said that there is some minor issue but no medication required. He suggested few things
- Dont Scold, if scolding is requried try keep your voice low so that child dont feel too scared
- take care of proper sleep at least 8 - 10 hours a day
- Proper and healthy food
He says its so minor that medication is not required and this will go away with time.

Please suggst if anyone have different opinion.

My daughter is going through this right now and we are taking her to the doctor today for further investigation. Watching your child faint and be so out of it is quite scary