My apple watch is too hot

I was wearing on my apple watch at the beach today although the battery usually last more , I was surprised that it went dead in the afternoon, when I came back at home I put it on the charger but after a 5 min or so I checked it and wasn’t able to turn off and was very hot with apple sign flashing every while, what’s that supposed to be? Is it battery? Heat? Overcharged? How can I fix it ? I even try to force reset but still nothing….