I passed out after the big "O" and fell the doctor said not to worry unless it happens a lot but he sent me to get a physical and blood work

And your question is?

Is it or should I worry or take certain pre-cautions

I would trust your doctor on this one. I've heard of it happening, but your doctor would know YOU better than we would.

It's good that tests are going to be done to rule out any physical problems.

Has it happened only once? Or everything you orgasm? I have blacked out briefly, i.e. 5 seconds or so, after an orgasm. Only happened once.

As your doctor said, unless it becomes a regular occurrence don't worry too much about it. Personally I would trust what my doctor says over what a bunch on yahoos on a website any day. This is why the vast majority of the answers here are "Go to a doctor," "go get counselling," for the more serious sexual disorders.

Thanks people ! Yes I will listen to my doctor but sometimes its makes you feel beter to know you are not the only one and thatother survived it Ha! Ha! Ha!

I have occaisonally had a strange OTT reaction after a particularly good orgasm. I have blacked out for a few seconds on occasion, burst into tears once or twice, and had a fit of uncontrollable laughting once. I fairly often get really weak and shaky for a few minutes, often trembling all over. I gather all these are normal reactions to have on occasion. No idea what the body mechanics are behind this but it does happen. I mention these other reactions since people who are particularly sensitive this way can experience any of these so if they do happen don't worry. If you black-out or have any other weird stuff at other times rather than just after sex then I would worry.

The French call orgasm 'La petite mort' - the little death - which kind of sums it up for those who are highly affected!