and then there's Helmet Headache.

I was riding and had a headache that kept getting worse. I stopped for a potty
break and noticed that it had gone from dull to excruciating, pretty unusual,
bicycling usually HELPS my headaches get better.
So i took off my helmet and massaged my temples, and it started to go away.
No, it WENT AWAY completely! the helmet was too tight...