Apple watch ultra dead after diving

Ive recently gone down to 21M diving, watch was working well, then suddenly screen turn off and not responding.

once out of the water the watch is dead, ive tried charging it, force restart etc and nothing.

I have noticed that once its been charging for a while it gets warm but id say that happens also prior to diving.

I didnt tamper with it or hit it with anything..

any one have any ideas?

thanks,

marcelo