I think it was a sleep deprivation headache. I had a faint one throughout work and figured a nap after work would help.
Which it did.
Though I was delayed with going straight home after work to meet with a friend.
But by the end of our visit.
I had quite the pounding headache by the time I was able to head home, right in the front of my head. Behind the eyes. 
Thankfully, a nap and a shower helped to make it mostly fade. Though it kinda lingered throughout the night.