Obviously, the thing to do for now is back down a bit on weight. When you squat next time. Be sure you are breathing correctly - inhaling as you descend, exhaling as you rise. I see a lot of people who tend to hold their breath during heavy lifts (me too). If this is the case you may be 1. Starving youself of needed oxygen, and 2. Building up internal pressures including blood pressure. When you stop, your blood pressure might take a plunge, along with oxygen deficiency - the result may be what you describe.