Physiologically speaking, a stroke occurs when glycogen stores are depleted to the point where they can no longer adequately supply working muscles with the fuel needed to produce energy or maintain blood glucose levels. As a result, your body has to take drastic measures to slow you down. Perhaps a complete stroke can be described as total glycogen depletion of muscles and liver. Glycogen is the primary source of fuel for endurance athletes.
This severe glycogen depletion does not occur during short-term, high-intensity exertion, but occurs during continuous exercise at about 70 to 85 percent of maximum VO2 that is maintained for periods of more than about two hours. The short answer is that having sex refers to low blood sugar (hypoglycemia) and simply running out of fuel for the body and brain.