I don't know what happened recently with GW5 but when my watch reaches 15% battery life it vibrates to notify me it's entering battery saving mode in the middle of the night when my sleep mode is enabled. I tried to look at the settings and while in sleep mode there are no notifications allowed. It happened to me twice in the last 2 weeks as I never happened since Feb 2023 when I bought my watch.
The obvious answer to your question is make sure that your watch is not going to get to this point of notifying you in the middle of the night. I have a Watch 6 and this is just a part of owning a device and making sure it can perform as designed to do. I always - when I remember check for battery capacity at night. Do you not make sure your phone is charged enough to make it through the night so do the same with your watch??
We all have to do our own part in helping our devices perform as they are designed to
