What makes someone gay? For Chris Birch, it was a stroke.

Messing around, doing forward rolls down a grass verge, the heavy-drinking 19-stone rugby-player "felt something go" in his neck. Momentary pressure had damaged a carotid artery, stemming blood flow to his brain and triggering a stroke. Over a year after the accident, Chris came out, claiming the stroke had changed his sexuality.

After agreeing to be the subject of a BBC3 documentary Totally Different Me, Chris welcomed filmmakers into his home in the Welsh Valleys town of Ystrad Mynach, where he invited an ex to pore over photographs of "the old Chris", to learn what he was like, and spoke candidly about losing touch with his mother. He found the programme, which was re-titled I Woke Up Gay, "Disappointing. I thought it would be more medical; I thought it would tell a more honest story."

Annually, one in four strokes will happen to people under 65. As part of May's Stroke Awareness Month, Chris spoke to VICE about his experience. "Initially I just thought I'd hit my head or hurt myself," he explains on the phone. "I was very dizzy, but you're never quick to diagnose yourself – you just power on and hopefully no one will notice."

First diagnosed with glandular fever, Chris experienced memory slips, slurred speech and numbing in his hands and arms, so paid to see a private neurologist. He was diagnosed as having had a stroke and prescribed daily medication, which he still takes. Palsy dragged on the left side of Chris's body, most noticeably an eyelid and a nipple, but his personality lifted. He bored of his clerical banking job: "I thought, 'I don't like this job any more; I don't see anyone, I'd like to actually meet people,'" and switched to sales. "I was very introverted before, but now I had more confidence and was less inhibited."

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The sexuality shift took longer, Chris explains: "When I realised I was gay, I didn't do anything about it for a good six months. I told my mother, which was bigger than I thought it would be; you go round the mulberry bush to say it – you think, 'Why am I doing this?' – and as soon as I told her, I thought, 'Right, that's sorted.'"

He avoided dating until meeting his boyfriend, Jack: "I wanted to make certain what I was thinking and what I was feeling was true and wasn't a temporary thing, or something that was mistaken. I thought: my left nipple was lower than my right nipple, will that go back into place? Therefore, will my sexuality re-align? It sounds really pathetic and silly to say, but that's how it felt."

The financial crash of 2008 prompted Chris to leave banking and pursue further education. All classes were full, bar plumbing and hairdressing, and he chose the latter, not aware how vital it would later be to his tabloid credentials.

A client at the salon recommended Chris tell his story to a weekly magazine, and he went for it: "I supposed someone might want to hear about me having a stroke and coming out the other side, and it may help someone."

Allowing the story to be syndicated as "a small article in a magazine inside the newspaper", it splashed across two pages in The Mirror, headlined "A Stroke Made Me Gay".

"It was a bit of a shock – it felt unnecessary," says Chris. "The salon had umpteen phone calls every day from people who wanted to speak to me. One lady in her seventies travelled an hour on the bus to thank me for telling this story."

"I can remember very vividly being very happy and content with being with girls on every level: relationships, sensual, everything. But now I look at those feelings as if they're distant and they don't belong to me."

Of the 1.1 million people in the UK who have had a stroke, over half are resultantly dependent on others for assistance with everyday activities. One in five strokes are fatal. However, the USP of Chris's story wasn't his survival, but that he was now gay, and attributed this to the stroke.

The underlying debate was clear: had a near-death experience provoked a closeted Chris to re-assess his identity while simultaneously being ashamed about his sexuality's true provenance? Or could a roly-poly really instigate a sexuality change? Though Chris now admits: "I know [after a stroke] you're reminded of your mortality and think you have to live every day differently, or as if it was the last. All I can say is that I am the proof [of stroke changing sexual orientation], and I'm not the only one."

He cites another gay man who became straight following a stroke, and pushes against accusations of lies by explaining: "Obviously there are portions of my life I can't remember, but I can remember very vividly being very happy and content with being with girls on every level: relationships, sensual, everything. I distinctly remember that, but now I look at those feelings as if they're distant and they don't belong to me."

He knows his story is far-fetched, but blames inaccurate reporting – such as claims his neck had broken, or he'd fallen into coma – for chipping away at its credibility.

Portrait of Chris Birch, copyright Birkenhaus Media 2017

In I Woke Up Gay, Dr Qazi Rahman, a researcher at Queen Mary University looking into "genes for sexual orientation", tells Chris that, based on some tests, it's likely he was born straight. Dr Rahman now researches mental health in non-heterosexuals, which reflects a shift in wider culture; since I Woke Up Gay, the UK has introduced same-sex marriage, "gay cure" therapy has been banned and diversifying visibility of gay men has trampled stereotypical notions of gay presentation.

Yet presently, many still consider homosexuality a choice, rendering the nature-nurture debate inevitably detrimental. Any discovery that homosexuality is learned makes LGB people look extravagant, putting their lives at risk for perverse gain. Fake news stories credited Chris as proof of a "gay cure".

"They were saying, 'You don't have to be gay. Look, this man wasn't gay before and now he's gay, therefore it's not from birth and we can correct it,'" he says. "They said I was a liar and gay all along, too. I was absolutely heartbroken. If there was a way of pressing 'delete' on the internet I would have done. Fake Twitter and Facebook accounts were set up in my name and they would go at odds with what I was saying and pick out every small detail. It was awful. I wish I hadn't said anything."

Professional writers joined in with critiques. In Gawker, Rich Juzwiak wrote: "Birch's story seems counterproductive to the equality cause." Keith Watson for The Metro posited: "The odd thing is, if he was really as happy with the 'new' Birch as he claimed – and he did look it, sweet boyfriend and all – then why was he so bothered about proving it was the coma [sic] that turned him?" And staff at Anorak wondered: "Might it be that inside every 19 stone rugby player is a homosexual hairdresser waiting to get out..?"

"I thought: my left nipple was lower than my right nipple, will that go back into place? Therefore, will my sexuality re-align?"

Chris now refuses to pay his TV licence or watch the BBC, and there remains an embargo on British sales of a German book he co-authored about his stroke. He explains: "I know I sound like I'm very bitter, but I'm not. The BBC really dumbed down the documentary to the point it was ridiculous. They forced the public to perceive that I woke up gay… it's very sensationalised."

Teaching hairdressing part-time while owning a professional cleaning business, Chris is still in a relationship with Jack, and lives with him and their four dogs – Chris says he never liked animals before his stroke – in Cardiff.

The brain is a delicate organ, and a stroke affects it in multitudinous ways. Chris didn't only survive, but has had the courage to live as a gay man in a country where one in six LGBT people experiences hate crime. Who cares how he got here – at least he's got the bravery to be who he says he is. What's gayer than that?

Visit Stroke.org to learn how to recognise the symptoms of a stroke and to find out more about Stroke Awareness Month.