I either got this from:
1. Pressing the arm against my body weight while getting up from bed. Or the floor. I thought I heard a snap.
2. Spraining the muscle from spending 3 days in a row sandpapering the excess putty on the front lip of Slow White Poke's bumper - a DIY moment gone wrong.
And this post was written entirely left-handed.
No, of course not. I cheated.
Another 16 hours to go.