and he said I had most likely strained my neck while lifting. So whenever my neck and shoulders would tense up
during a particularly strenuous rep, the strained nerves in my neck would cause a headache. He said if I just quit working out for a while and gave my neck a chance to heal, I would be fine.
In any event, I stopped strength training for a couple of months, and when I started up again I was okay. Previously I had tried taking a 2 or 3 weeks off, but it wasn't enough.