Giuliano Pirone, 33, was working out in a Perth gym when he felt unwell and made his way to a shower cubicle, where he collapsed early on August 20.
Mr Pirone's family raised the alarm about 3pm and police used the signal from the building supervisor's mobile phone to locate him.
Officers broke down the bathroom door and found the father of a young daughter slumped on the floor under cold running water about 10.30pm.
He never regained consciousness and an MRI confirmed he had lost brain function.
Mr Pirone was in an induced coma on life support at Joondalup hospital for two weeks before he died, ABC Radio reported on Friday.
Doctors believe Mr Pirone's blood sugar levels became extremely low and his blood pressure dropped, potentially triggering a seizure, his family said.
Mr Pirone's family wants to know how he could have been in the shower for so long without anyone noticing he was there.
"My beautiful son was alone on that floor, collapsed, smashed his head for about 15 hours and no one noticed anything," his mother Daniela Pirone told the radio station last week.
"His car was parked right at the front of the gym because when he checked in, it was 4:55am.
"The showers are 20 metres away from reception and no-one noticed anything. Don't the showers get cleaned? I'm just dumbfounded."
Ms Pirone said CCTV footage showed her son on a treadmill "not feeling too good" before bumping into other equipment in the gym.
"He staggers to the showers, holding his stomach," she said.
"[He] must have just locked himself in, felt hot, turned the cold water on and bang, he collapsed."
Mr Pirone's sister, Rosa Ostapenko, has created a GoFundMe page "to help give her (three-year-old niece) the life her daddy would have given her".
"He is loved by his family and friends. He was the light as soon as he walked through any door. He would give you the shirt off his back," Ms Ostapenko said of her brother.Â
"He was training for his first bodybuilding competition and was two weeks out and he was so excited.
"If he was found earlier he would have had a higher chance of survival and living his best life. Sadly my beautiful brother lost his fight."
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