It may have been a delayed reaction to the stress of having a busy day at work. 
An unexpectedly crazy busy day at work because I'd forgotten it was a holiday and the day before the superbowl.

So I was kept pretty busy running to and fro and helping customers and keeping track of coworkers and such. 

It makes sense that after I've been home for a bit and focusing on writing and such.
That I would end up tensed enough in the shoulders -specifically the left side to gain an unwelcome headache behind my left eye. *exhales* 

It's only settling in now.
But hopefully I can keep it down and at bay.