A Guernsey diver who sparked a false alarm over his disappearance suffered a mental breakdown, his family believes.
Mr Harvey and wife Katie face a "tough time" say relatives
Matthew Harvey, 35, went missing from Fermain Bay on Saturday and was picked up by a yacht nearby on Monday.
A major search was launched, but it emerged on Thursday that he had taken a ferry to the UK, then returned.
The reason and destination is still a mystery, but father-in-law Vic Dorey said: "There is obviously some sickness problem somewhere."
He told the Guernsey Press both families believed Mr Harvey had suffered a mental breakdown.
Vic Dorey said: "It would appear to be a breakdown - what else? The mind is a funny thing, breakdowns happen."
He said it was going to be "very tough" for museum worker Mr Harvey and his wife Katie.
"With time we will try and see it through and help as much as we can.
Mr Harvey was found floating off Fermain Bay on Monday evening
"Both sides of the family are supporting them 100%. What alternative have we got?"
After his rescue on Monday, Mr Harvey claimed to have been knocked unconscious and stranded on rocks for two nights.
However, after a member of the public in the UK alerted police, inquiries revealed that he had taken a ferry to the UK on Saturday afternoon, returning on Monday morning.
He then went back into the sea and was found by a yacht crew in the sea off Fermain Bay.
Guernsey Museum worker Mr Harvey has been interviewed by police, but no decision has been taken on whether any action will be taken against him.
It is understood that the search operation to rescue Mr Harvey cost at least £10,000.
'Cry for help'
At the time of the incident there were several hundred people searching for Mr Harvey, including teams from the RNLI and coastguards as well as friends and family.
Staff at a self-storage centre in Poole, Dorset, have been helping Guernsey Police with inquiries, after they claimed to have seen Mr Harvey on Sunday and again on Monday.
They said he came into Poole Lock and Store and left diving equipment which has not been retrieved.
Police refused to comment on claims Mr Harvey was seen strolling through Bournemouth.
Insp Trevor Coleman said: "We know where he went and what he did and we're satisfied it's true he did leave the island."
Mr Harvey's father suggested his son's bizarre behaviour was a cry for help.
Dan Harvey, 66, told the Daily Mail: "He just flipped. He just lost his mind.
"It was some sort of breakdown. He just decided to get on that ferry in a moment of madness.
"To get back into the water like that at twilight was a cry for help.
"The balance of his mind was disturbed. He told me that he has no recollection and cannot account for what he did."