Former Olympic swimming champion Grant Hackett was arrested in Australia after his “raving and ranting” forced his father to call police.
However, the troubled 36-year-old, who has struggled with prescription drug problems, was released without charge.
“Grant’s got a medical problem and it manifested itself here this morning,” the Australian’s father Neville told the Gold Coast Bulletin newspaper.
Last year Hackett apologised after clashing with a passenger on a flight.
A Queensland Police spokesman said Wednesday’s arrest followed reports of a disturbance, but would not give further details.
But the 10-times world champion’s father told the paper: “He’s been receiving treatment from a doctor. He’s big and powerful when he’s not happy.
“We decided he needed some treatment but there was no way he was going to go and get treatment this morning, so we called the police.”
Television footage showed Hackett displaying his handcuffs to waiting cameras as he was driven into a police station.
His family told reporters they had concerns for his welfare.
“This is not Grant Hackett,” his brother Craig said in footage broadcast by Nine News.
“This is a completely different person. I don’t know this person, my mum and dad don’t know this person.
“He’s there in body but he’s not there in mind, soul or spirit.”
Hackett, who won Olympic gold medals in the 1,500m freestyle and 4x200m freestyle relay at Sydney 2000 and in the 1,500m freestyle at Athens 2004, had a long-standing rivalry with compatriot Ian Thorpe.
He returned to the pool last year to make an unsuccessful bid to qualify for the Rio Olympics.
He was questioned by airport police in Melbourne last April after allegedly assaulting a male passenger over a reclined seat on a flight. Hackett said he had been drinking in the wake of his Olympic disappointment and publicly apologised.
Hackett has previously admitted he became dependent on a sleep medication.
The swimmer flew to the United States in 2014 to spend time in a rehab centre after he was spotted topless and disoriented in the lobby of a Melbourne casino.