I would lean towards his blood presure getting too high. Is he taking any kind of stims or supps that would increase his heart rate and blood pressure? Did he just start taking something before last wednesday. Your blood pressure goes up during periods of stress (training) and increased heart rate. Obviously during a heavy taxing set of anything that gets the heart pumping good, BP will go up. If he just started taking something new, I would suggest stopping it. It is something that would require a PCT, then do it correctly, but now. If it's a stim of some kind, then just stop. Don't take it for a few days and see if same symptoms occur. He should also get his BP checked. Ideally, best time is in am after waking to get true resting BP. He can get a basic BP monitor to do that at home. If his resting BP is high, then it is going to be higher when lifting. If he hasn't changed anything as far as new supplements, then he should see his doctor regardless. Lifting hard and heavy shouldn't create so much pressure that everytime he gets a nasty headache. It could be a serious underlying condition that needs to be checked. A possible brain aneurysm or anything remotely close to that is VERY SERIOUS and should be checked!