I'm a star
Where I am you can definitely take an extended break or a second break if its hot out, but letting your supe know what's going on seems like common sense, if for nothing else than to cover your ass.
My full-time supervisor is a hard ass and if somebody in my area went AWOL while the dock was ed up as the belt stopping "a lot and for long times" would suggest, he would definitely walk you out for stealing time or job abandonment or something.
Op did as soon as he got back. If he was heat fatigued and needing an extra long break is he supposed to interrupt that to go find his sup to ask permission? No.