What are my blackouts due to?

I've been getting split second blackouts when i eat for 15 years. i'm 100% healthy otherwise. im taking anemia tests and want an epilepsy test for petit mal..i think heat triggers it...when we eat our temperature changes...also when im in a hot room i feel similarly light headed. its like a head rush..a wave comes over me and everything goes black for split seconds. i can have it a few times a day or not at all..mainly when i eat. stress seems to trigger it too. i read it could be jaw clenching which is interesting.....i wish i knew the answer to these annoying black outs!! anyone else have the same thing or know the answer? the doctors are baffled and of no help so far. someone mentioned gas boiler poisoning which is interesting as i sleep in a room that has a gas boiler..but then why would i get a blackout when i eat every time!!