Shoulder Blade... Shoulder Blade... Why Hurtest Thou Shoulder Blade?

As I type this... my shoulder blade is killing me.  It's been getting better, but today for some reason, it's screaming at me.  I have my theory as to why this is, but perhaps... it's all in my mind.

I know that when I tense up, it starts to hurt.  I started tensing up at 9:30 this morning.  UGH!

Well, it's my Friday today, and I won't have to deal with what I've had to deal with today for four days, so I can get some rest.

But...

Shoulder blade... Shoulder blade... Why hurtest thou shoulder blade?