Na-adjective (keiyodoshi), Adverb taking the 'to' particle, Suru verb
completely exhausted; dog-tired; dreadfully weary; terribly frustrated; limp; weak; flimsy
Onomatopoeic or mimetic word
山道で迷って、ヘロヘロに疲れて家にたどり着いた。I arrived home, thoroughly worn out, after getting lost in the mountain paths.
Also written へろへろ