One thing that may have led to this episode: A recent shoulder surgery.

I've been battling a left shoulder injury for about 15 months. Doing lots of left side rehab. LOTS. There's been a lot of stress around the left shoulder and anterior chest/neck area for a while now. I finally threw in the towel five weeks ago and had it done.

I was immobile and packed with ice for some time. Then had limited shoulder mobility. It's gradually gotten better to the point where five weeks later I'm getting somewhat back to normal. That said, I wonder if the restricted mobility contributed here.