I find that sometimes I get dizzy immediately after exercise, and my current theory is that getting hot from the exercise causes the blood pressure to drop a bit, and if I stop working out cold-turkey in that condition, there will be a short period of dizziness as my body re-adjusts to less exertion and a lower heart rate. I've noticed that if I jog lightly in place, or just move around in a wiggly way, that it will hold off the dizziness until I've returned to normal. (As normal as I get, anyway.)