Apple Watch not turning on and getting hot while charging

This looks like a defective battery. Has the watch been exposed to water lately?

Has the battery ever been replaced by Apple?

If it is getting hot, don't continue to charge it, and get it inspected by an Authorised Apple Service Provider or Apple Store next to your place:

Apple - Find Locations

Your battery each the end of the usable lifetime and needs to be replaced.

If you are willing to pay the service fee for the Battery Service, Apple will usually replace your watch with a new unit.

You can get an estimate on the Apple Watch Service page:

Apple Watch Service and Repair - Apple Support