It was probably the stress from the day before. Maybe not enough sleep.
But I ended up with a nuclear headache behind my left eye today after fighting a minor headache that had lodged behind my eyes that I was certain was from just being tired.
But after a nap the headache had morphed into the nuclear migraine.
I ended up spending most of the rest of the day on the couch with soft tv sounds on in the background and occasionally getting up to either heat up my heat pack or to take a shower to try and relax the tense muscles in my neck.

Finally close to midnight I was successful in getting rid of it.