Looks like my Apple Watch troubles may simply be a band that isn’t tight enough. I’m still using the original sport band, but just moved to a tighter notch and HR seems to be stable. It didn’t feel like it was that loose, but apparently it was.

I was actually so concerned about the alert the first time it came up (which was last week) that I went to a clinic. Had a full EKG, blood work, and everything. Nothing wrong at all. I’ve had the watch over a year and it’s been fine, but now I can’t trust it.