When the battery health goes down, the battery issue starts to need to charge again and again. So always need to avoid charging any device for a longer time; once 100% charged, disconnect the device and not keep on charge.
Most of the time, this kind of issue occurs when the battery is bad. As a result, it doesn't hold the charge when the load comes on the device.
Only the reason I believe that the screen comes out when the battery swell, I guess at the same time are you experiencing the battery is dying quicker. Then for sure, there is a battery issue.
When your experiencing the health of your iWatch is down, when you see the battery is draining faster than before, or your Apple Watch taking longer time to charge. These are some symptoms of batteries getting bad.