Apple Watch battery draining overnight

Is anyone else having rapid battery drain overnight? Two weeks ago I traveled internationally and in the 5 days since my return my Apple Watch battery drains overnight. I use it to track sleep, so I charge it fully before bed, wear it, and wake to find it only has 10% battery left. Prior to this trip, I would awake with ~50% charged. I used it throughout my trip as my cell plan covered the area I was in.

A couple days ago, I went through the background app refresh list and turned off a few that were unnecessary and that night the watch behaved as normal. But this morning I woke to 10% charge again. 

There are no new apps installed, and nothing significant has changed with my habits. While traveling I didn't use the alarm features that I use at home (built-in alarm + Auto Sleep haptic), but I can't imagine that making a significant difference. I keep my phone in a different room, but that's been the case for years. I have noticed more than once this week that my phone alarm is going off when I get up which suggests that the watch / phone stop communicating at some point during the night. 

It's a Series 5 (A2094) running the latest version of watchOS (9.3.1). Battery Health shows that the battery has 81% capacity, so I know it's getting older and won't perform like it's brand-new, but this is a significant change without any explanation.

I am going to do the whole unpair > erase > re-pair today to see if that helps, but I figured it was worth asking if anyone else has noticed this too.

I really wish you could see which apps were using the most battery on the watch like you can on your phone!