Disclaimer: Personal medical topic.
On a couple occassions in my life I have almost passed out. The events proceeding them have been similar, so maybe I can learn from the whole experience. The general pre-conditions for me are (1) lack of food prior to the event, (2) paying an extreme amount of attention to whatever I'm doing at the time of the event, and (3) usually, I've locked my knees, restricting blood flow in my body. According to proctologists, it is also relatively common occurance during exams given to patients.
It turns out I likely have a strong a vaso-vagal response. While the symptons are not always identical for different people, they typically include feeling light-headed, nausea, perspiring, fainting, and loss of bowel and bladder control. I do not feel all of these symptoms, but just a couple is enough; trust me.
Clinically, this is combined with an expansion of the blood vessels in the legs and loss of blood pressure, which means I turn as white as ghost. All of which makes it hard for Kristi if she happens to be nearby; she is understandably scared when I suddenly turn white, feel faint, and look like I'm about to become unconcious.
Apparently, the condition is not serious and there is no risk of health consequences. Even so, I have to agree with some of the folks who have discussed this online; being told to sit with your head between your knees just doesn't seem like an adequate medical response.
Additional links at: MayoClinic.com, Health Encyclopedia
In other personal medical news, I am going to have a colonoscopy next week. Goodie, goodie.