These are exertional headaches. They are usually benign. They are somewhat load related but they can also be volume related. In other words they have to do with how much you exert yourself. Breathing can play a role, so if you hold your breath that can lead to them but if you get them it does not mean that you have held your breath. Posturing of the neck (like jutting your chin forward) can also be a factor. Always try to keep the neck neutrally aligned.
Since you have it right now you will pretty much need to take a break or it won't go away. I'd say at least 3 or 4 days or else you're going to find it wanting to return. Basically a feeling like your about to get the pain and then if you keep pushing it all of a sudden your in agony. So take a break to let it get better then you'll want to probably drop the weight and the volume a bit and build back up.
You may feel it wanting to return at first. Breathing can help. One trick is if you feel it starting to come back (even with the ligher weights or whatever) pause at the top of the rep and take some very quick little puffing breaths. Like women do when they're having babies. I'm not kidding
. This may help re-equalize the intra-cranial blood pressure. It used to work for me like a charm.
Once you have managed to get the weights going again and as long as you don't overdo it, after a little bit you should be past it and you won't have to worry about it for the most part unless you make sudden huge changes in weight or volume.
If it's hurting all the time right now go ahead and take something for the pain. It should at least take the edge off.
Oh, and try not to go up and down too fast on things like squats or deads.
If this doesn't go away in a few days or keep coming back, see a doctor!