You may have put too much stain on your traps causing pressure on the blood flow or nerves running up your skull. I sometimes get a sharp almost electrocuted pain up the side of my neck into my head. Just happens out of the blue. Hurts like hell.
They also call them tension headaches for a reason. All those muscles and nerves running along the cervical portion of your neck can cause all sorts of problems.
I was rear ended in an auto accident 10yrs ago. Total'd my car. I have recurring issues with my neck, and right scapula area from time to time. I've got a decent Chiropractor that gets things put back where they go, and I'm pain free till things degenerate again. Havn't had many isues since I started lifting again, and keeping myself stronger.
My Sister is a DC., Although she no longer practices. I wish we lived closer, because she really knows her stuff. I hate finding new DC's. When I find a good one, I stick with them.
Definately back off a little, if you've been hitting it at the 90% for a while. Don't wan't to stay in that regime too long. Hit it, then set a new % to work back up from again.
Don't want to find yourself on the disabled list.