Hong Saengoen, 54, selected a woman at a brothel in Phuket City's notorious Soi Eleven, Poonpol, paid his 500 baht and went to the bathroom to change.
The woman hopped into bed and waited. When Khun Hong did not emerge, the woman investigated.
Police said she found Khun Hong slumped in the change room, dressed in a towel and clutching his clothes.
There were no suspicious circumstances, said investigating officers from Phuket City. The body was taken to Vachira Phuket Hospital.