Stretch yawn faint
Occasionally I'm overwhelmed with the urge to have a really good stretch, tensing my muscles until they tremble, tipping my head back and unleashing a full on yawn. Lately this is followed by a faint spell - the world goes distant, my vision fades, and everything gets a bit woozy. After a few breaths the world re-intrudes, and normality resumes. It hasn't concerned me, but after a particularly strong episode today my curiosity was peaked, and I typed 'stretch yawn faint' into Google (hallowed be thy results, for thine is the engine, the spider and the crawler) to see what cropped up. It turns out the combo of stretching and tipping the head back starves the brain of oxygen. The stretch lengthens the blood vessels causing a blood pressure drop, whilst it also creates demand for oxygen in the tensing muscles, and finally the head tip constricts an artery in the neck which cuts off the blood to the brain. I'm not sure how common it is in absolute terms, but the f...