A "COURT jester" who danced at one of Colonel Gaddafi's compounds was found dead in Swansea three weeks later, an inquest heard.
The cause of Martin Longhurst's death was unascertained, partly because he died up to eight days before being found in his city flat.
Mobile phone records showed he had bought Valium, traces of which were found in his system.
Pathologist Dr Maurizio Brotto, who carried out the post mortem, speculated that stressful events during and after Mr Longhurst's bizarre trip to war-torn Libya were a possible factor in his death.
Mr Longhurst's mother, Anne Taggett, said her son changed from a "happy-go-lucky" character to "a hell of a mess" when he returned from Libya towards the end of April 2011.
"He was not the same Martin," she said. "I said to him, 'What happened out there, Martin?' He would not tell me."
One of her son's friends told her that he had been beaten up in prison, but Mrs Taggett said she saw no obvious marks to confirm this, an observation backed up by Dr Brotto.
"I know they locked him up," said Mrs Taggett. "They thought he was a spy. Martin couldn't spy for nobody."
In a written statement, Detective Sergeant Stuart Prenderville, of South Wales Police, said Mr Longhurst had travelled to Libya via Tunisia on April 9 as part of "an impartial, fact-finding mission" called British Civilians for Peace.
It was during the time that Gaddafi was clinging to power as opposition forces, backed up by Nato war planes, closed in.
Mr Longhurst's behaviour on the trip was described by a colleague, Ishmail Blagrove, as inappropriate.
"He was a court jester, making jokes and acting erratically," he said. "He spoke openly of his drug use and criminal past, and was actively searching for cannabis."
At a Gaddafi compound, the group was encouraged to take to the stage during a rally in support of the late dictator and be interviewed on television. The group voted not to. Shortly afterwards, Mr Longhurst climbed on the stage with a scarf draped over him and "was dancing enthusiastically".
These actions were said to further ostracise him from the group, and he left them to return to Wales on April 16. DS Prenderville said Mr Longhurst then contacted the UK Arab Society, which was behind the mission, telling them he wanted money not to sell his story to newspapers about the trip being "stage-managed as a (pro-Gaddafi) propaganda exercise".
Mr Longhurst described his experiences in an article published by this paper on April 20, for which he was not paid.
In it, he said he was held at a police station in the Libyan capital, Tripoli, and accused of trying to smuggle videotapes out of the country. He said he was terrified the authorities had got hold of an interview in which he had criticised the Gaddafi regime. But he was allowed to leave.
DS Prenderville said Mr Longhurst also spoke of a bottle of liquid he had picked up on a road out there. Back in Wales, Mr Longhurst texted a friend to say, "I'm getting ****ed, I've just come back from a war zone, lol".
His phone records suggest he bought Valium from a man on Swansea Beach. A text on April 23 said, "I'm Valium-ed up now".
Two days later he told a friend over the phone that he was "off his head". It was the last known contact with him.
On May 3, worried neighbours in St Alban's Road, Brynmill, saw an outline of a body through his bedroom window, and police scenes of crimes officers attended.
DS Prenderville concluded there were no suspicious circumstances surrounding his death, and the investigation ended.
Mr Longhurst had a younger sister and brother and had lived in Clydach, Neath, Port Talbot and Swansea before renting the St Alban's Road flat in 2009.
He had worked as a glass factory assembly worker, but served prison sentences for acquisitive offences relating to a cannabis and drink habit.
Recording an open verdict, Swansea Coroner Philip Rogers said he didn't think any Libya-related stress "can be related directly to his death".
He added: "There is no evidence that he had sustained any injuries.
"There is some evidence of him picking up something on the road, but nothing to suggest he had been poisoned by chemicals."