Alvamadeo, I'm not a physician. I'm a third year medical student. My husband is a cardiopulmonary physician but he's on call tonight and not here. We do have a mod who is a physician who may come through and see this and give his opinion one of these days.
The fainting you're describing is most likely something called vasovagal syncope. I know this not only because I've absorbed a lot of circulatory medicine over the years from my husband and studied this in school but also because I have it myself on occasion. Here's a link about it:
Vasovagal syncope - Wikipedia, the free encyclopedia
Basically what happens is a stressor of some type triggers an area in your brain that then triggers your parasympathetic nervous system, which basically "retreats." As a result, your blood pressure drops. In some people, the heart rate drops. In others, it doesn't. But what happens with the quick drop in BP is a brief loss of consciousness.
In the vast majority of people vasovagal syncope is harmless, but in a small, small group--and this group is actually having a slightly different type of syncope, but the symptoms are the same--fainting could be a sign of a serious problem with your heart rhythm called "long QT syndrome." This problem can be genetically carried, so if you know of others in your family who've had to be put on meds or have an implanted defibrillator installed for a potentially deadly heart rhythm, you should get to your doctor and get your fainting episodes further evaluated (with an EKG and a thorough history).
The part of your question where you ask about heart attack risk and cannabis is a completely separate second question. We're really not talking about "heart attacks," which is a medically ambiguous term, when we talk about fainting. The type of cardiac event involved in long QT syndrome is cardiac arrest, where the heart goes into a deadly rhythm and then simply stops. Your fainting in the instance after you'd used cannabis was likely caused by a quick alteration to your blood pressure. It could have spiked up or fallen suddenly. In your case it likely fell. Either way, it stimulated your parasympathetic nervous system and you lost consciousness temporarily. Probably harmless, but if you have the genetics for long QT syndrome, that's not something you'd want to let go unevaluated.
As the information you copied above says, the frequency of cannabis causing heart attacks is unknown because it's not been studied and because people who die of heart attacks can't come back to tell us whether they'd just been smoking it. Since it's an illicit substance in most states, its frequency of use isn't really known. What we do know is that, in people for whom certain strains or simply the act of smoking raises blood pressure, that can trigger a "heart attack" or a stroke. Probably these are people who already have a history and risk of heart disease. We also know that the smoking of cannabis isn't great for people's hearts or lungs. Not because of cannabis' active ingredients--if you could take those by themselves they'd be beneficial--but because of the act of smoking itself. In people at risk for heart disease, inhaling burning vegetable matter and the other particulate crap in the smoke competes with their oxygen intake, irritates the lungs, and can do bad things to vascular elasticity and plaque buildup. Again, it's important that we're real clear here. This is from the act of smoking burning vegetable matter, not the active ingredients. Vaping and eating cannabis are much heart-healthier alternatives.
Till you get yourself seen about, it'd be wise for you not to smoke anything. You also should avoid exercise and/or great stress. You have only a tiny chance of having the long QT syndrome, but till you know, it's important that you not risk bringing it on.
Sorry for the long answer! I'm now having to be able to explain stuff like this when professors and interns and residents put me on the spot during my rotations so it was a good teaching review for me. Hope this helps.
