Woke up with a slight headache behind my right eye today.
I think it was from not getting the right amount of restful sleep as I ended up tossing and turning most of the night. 
I think it was because the place we're staying at may have gotten a little warm, and I don't usually sleep well if the home is too warm. 

So I think that was the main reason why I had the slight headache.
A heatpack, some advil, and a distraction later, helped to make it go away.