Thanks, Bruno75. I appreciate your detailed message. My watch is up to date since that update last week. I just updated my phone. (Not sure why it wasn’t up to date, since I have auto update on.) Since no visible notifications accompany the ding and vibrate, I wouldn’t know what to turn off in Notifications, but I just went in and turned off a lot of app notifications for apps from which I’ve never received notifications! I have no alarms set. Perhaps my phone update will cure the problem, though this recent OS seems to be designed to deal with security issues, not bugs like mine.
As for Focus/Do Not Disturb, I set that on my phone, not my watch. I don’t see where (if anywhere) to set it on the watch/watch app. The setting on my phone has—until recently—has applied to my watch, protected my sleep from noises and vibrations. That’s why the first ding was so surprising. And profoundly annoying.
Thanks again. I welcome any other suggestions.