I'm posting this not for medical advice but on the off chance of any similar experiences really.
My 2.5yr old (at the time) DS started to have these funny episodes where he would suddenly crumple and go limp for a few seconds (maybe up to 30 sec) he was still conscious but a bit dazed and sometimes would say "can't get up" and be totally limp then would abruptly come round again, get up and walk off as though nothing ever happened. It always tended to be in over excitement eg a lot of the attacks were on a swing, some running around etc.
This hasn't happened for 18 mths now but recently on holiday in the busy/loud swimming pool we think it happened again (it's sometimes hard to tell).
He was discharged last year from the paediatrician without any real answers.... tests on his heart came back fine, they ruled out epilepsy and didn't seem overly concerned and suggested an inner ear issue.
I still just feel anxious though, especially if it is coming back again and wondered if anyone has ever experienced anything similar?