After 10 days of my headache I was advised to go see an Upper Cervical Specialist because more than one person I spoke with felt that when I fell asleep, I fell asleep at an awkward angle and somehow did something to my neck.
Well, lo and behold, I went to see the specialist, he x-rayed me and found my atlas bone way out of alignment. He did an adjustment and the next day I woke up with no headache. Next day it came back for about two hours, I went back and he did another minor adjustment. Since then I have had fleeting headaches, but nothing major. The last two days I have had zero headaches.
I will never understand the human body, nor will I try to. All I can say is that I'm glad that I'm O.K. now.