A Saudi man living in the UK had been feeling homesick, an inquest was told.
Harith Alsharif moved to Southampton to be a chaperone for his sister, Malak Alsharif, while she studied for a PhD in the Hampshire city.
His body was found in the Itchen river next to Northam Bridge on August 5, 2021.
His sister said she did not believe her “soulmate” had taken his own life.
“I am shocked at what has happened,” she said.
In a statement read to the Winchester hearing, she said that in the weeks before his death, Mr Alsharif had become "more emotional” and wanted to return to Saudi Arabia.
She said her brother, who had previously gone missing for 10 days, had not slept for two days before his death and would go for long walks.
Ms Alsharif also said he once asked her if she had heard a voice he had apparently heard.
“He started to behave differently to how he used to be," she said. "This was the feeling of anxiety, he wasn’t feeling emotionally well here and wanted to go home as soon as possible.
“He felt anxious and didn’t want to stay in one place, which is why he went walking.”
Ms Alsharif said her brother had returned the previous day from a walk and had been “delighted and excited” to have found a river with restaurants along the waterfront.
She last saw him when he went for another walk the night before his body was discovered.
Recording an open verdict, Hampshire coroner Christopher Wilkinson said: “Suicide can never be assumed. The only evidence I have is Mr Alsharif entered the water voluntarily but there is no evidence he intended to take his own life.
“Given the peculiarities of his absence from the property on a number of occasions, I do wonder if he intended to enter the water while labouring under some form of mental illness at the time.”
He said he believed Mr Alsharif suffered cold water shock or hypothermia, leading to him getting into difficulties in the water.
A postmortem found that Mr Alsharif died as a result of immersion in water possibly caused by cold water shock or hypothermia. The examination found no alcohol or drugs in his system.
Detective Sergeant Caroline Price, of Hampshire Police, told the hearing that Mr Alsharif’s clothing was found on the river bank.
She said there was no sign of a struggle and she believed he had entered the water voluntarily.
