Why am I seeing a bubble animation with a count down timer on my Apple Watch Series 7?

(See attached photo): Screens like this example keep popping up on my (series 7) Apple watch. It's a countdown of sorts--colorful, sparkly, animated background--that starts at a random number and ends with a random number. There seems to be nothing in particular I'm doing to activate it. There also seems to be nothing I do to have it end with a "You Did It!" screen. I don't get any alert about it; I only know it's going on if I should happen to glance at my watch at the time it's happening.

Can someone tell me what on earth this is?

[Re-Titled by Moderator]