Today I set out to do intervals and had to stop when I started my first set because almost immediately I got a slamming headache. I took some slow spins around a side street and eventually worked back up to intervals and completed all that I had planned.
What could be the cause? I am a healthy 24-year-old, was just coming off a rest day, and it was a beautiful partly cloud 64 out when I left the house.
Has this happened to anyone else?