Ed O’Brien believed Radiohead’s turbulent years were behind him. It was 2001 and the guitarist and “band mum” had tamed egos, anchored stressful tours and clung tight as his bandmates swerved into electronic music. Now, the five-piece had nothing to prove, and he had slipped underwater. “I took St John’s Wort, a herbal antidepressant,” he recalls. “It scared the fuck out of me. It numbed me.”

O’Brien, now 51, was numb to everything back then, except for chronic back pain – a cruel irony for the child from a family of osteopaths. To recuperate, he and his girlfriend flew to Brazil, where they met a pair of friends. An encounter with a healer, they told him, may have saved their lives. He took the address.

“Going to a healer was against everything I grew up with,” O’Brien says, speaking from self-isolation in Wales (he is now healing again, this time from suspected coronavirus). “I told friends and family, and they’re like: ‘You’re fucking mad.’ In Britain – especially a place like Oxford – that’s the realm of fantasists.”

The healing resembled an intense therapy, drawing from wisdom similar to “Celtic spirituality, these old connections”. When it was over, “I wanted to share this profound experience with the world, and of course it’s thrown back in your face.” Still, leaving Brazil, he felt childlike. He remembers thinking: “Magic exists!”

Last December, O’Brien, under the name EOB, released his debut single, Brasil, a folktronica odyssey inspired by the country’s music and magic. The single precedes the release of Earth, a new album made with a band including the Invisible’s Dave Okumu, top-flight jazz rhythm section Nathan East and Omar Hakim and producers including the U2 and PJ Harvey collaborator Flood. Elsewhere, Laura Marling duets on a Celtic ballad, and a clutch of rave-rock tracks nod to Primal Scream’s Screamadelica. As if to declare independence from Radiohead, O’Brien opened his first gig with a cover of Layo & Bushwacka!’s club smash Love Story.

His songwriting aspirations go back to 1996, when Radiohead embarked on OK Computer. He planned to propose some material of his own, before self-doubt – and deference to Thom Yorke and Jonny Greenwood – got the better of him. Making Earth, “I kept asking: what would they think?” he says. “But that was stopping me stepping fully into me.” Has Yorke heard the album? “No. Philip [Selway, drummer] asked, so I sent it to him. But I wouldn’t want to do the U2 thing” – smuggling music unbidden into people’s phones. He smiles evenly. “If they want to hear it, that’s great. And if they don’t: whatever.”

Radiohead met at school in Oxford. O’Brien’s parents split when he was 10, in an era before people realised “the trauma on the children … I think that’s when music became my refuge.” When he wasn’t cradling his Sanyo portable cassette player, he gravitated toward cricket and theatre. In a school production of A Midsummer Night’s Dream, he played the charming Lysander; during a rehearsal, the misfit scoring the play swore at the teacher, and in Yorke, O’Brien found a fellow outsider. As he remembers it, the moment they decided to form a band is when his life came into focus.

As Radiohead rose from oddballs to celebrity refuseniks, O’Brien stayed grounded; he upgraded his mother into Madonna’s seat at a 1997 gig to improve her view. His supporting-actor good looks charmed reporters, which perhaps fuelled the band’s tall tales of his transgressions. For posterity, he denies angrily flipping a table at an LA restaurant (“nearly, though”) and – through appalled laughter – discovering brawny US rock while touring American strip clubs.

Radiohead c2000 ... (from left) Ed O’Brien, Jonny Greenwood, Philip Selway, Thom Yorke and Colin Greenwood.

In another anecdote – told by Yorke, seemingly to divert a prying reporter – O’Brien is said to have got so belligerently drunk after a tour that he drove a housemate to walk out. Considering this, O’Brien stutters, and I tell him I hadn’t meant to trivialise the story. “No,” he says finally, “it was actually ... thank you for saying that, because it was when I was very depressed.” His four-day lapse had followed the notoriously tense OK Computer tour. “One of my roles was always to be there for Thom,” he says, “because if he couldn’t get through it then none of us could. So I tended to put my own situation on the back burner. When I got back, I did the classic thing: I drank stupidly.”

O’Brien quit drinking in 2000, then began “culling” bad influences. “We didn’t have a big social life, Radiohead, so there weren’t many friends to jettison,” he says with another vague laugh. More troubles snowballed. As Yorke and Greenwood toiled with electronics for Kid A, he succumbed to a “creative paralysis” that “scared the living daylights out of me. When you see Thom come up with Everything in Its Right Place, playing on his Prophet [synth], you go: ‘Oh my God, can I do anything that will complement this?’ I’d brush it off with humour but inwardly, I was like: ‘I’m going to be found out.’’”

The Brazilian healing experience set him back on course. He took up yoga and attended protests for the first time since university. In 2018, when Extinction Rebellion formed, he became an informal patron. (Radiohead raised roughly £500,000 for the organisation last year.) Citing its decentralised leadership and “pan-generational” appeal, he broadly considers XR “incredibly enlightened. There have been a few renegade issues, but as Naomi Klein says: ‘Activism is messy.’ At 51, I’m more like a teenager in my idealism than I’ve ever been.”

As he fights his coronavirus symptoms, he wonders if there might be an environmental legacy from the outbreak. “If you look at history, it’s calamities that awaken us to what’s important,” he says. “Who’s gonna win the Premier League is no longer an issue, and that comes from a football fan. I always think about the second world war, the way the country mobilised behind one thing, defeating Nazism. I’ve always felt that the climate emergency will force that upon us. And unfortunately, I think that humanity has only really learned from disaster.”

O’Brien performing in March. Photograph: Jim Dyson/Getty Images

He returned to Brazil with his family in 2012, this time for a year. He told his Radiohead bandmates: “If you’re in the creative flow, carry on without me,” maybe sensing that, on his family’s quiet Brazilian farm, he would begin noodling towards his solo LP.

Doubts persisted, however. One evening after a Radiohead tour, O’Brien revisited his half-finished album and panicked. “You fucking idiot,” he remembers thinking. “You wasted all these people’s time.” An overreaction, but a motivating one. “My mantra became: What is your truth? What do you really feel?’ When I found that, everything else went out the window: ‘I don’t care that you don’t like this, Flood!’”

I remind him of a 2001 radio phone-in where a fan asked if he would ever sing lead vocals on a Radiohead song. He laughed it off then (“I bloody hope not”) and, another time, joked that an Ed O’Brien record would be “ethereal music” for stoners. “The person who said that had a lot of fear,” he says today. “The band [has] a tough love thing, which is great. But sometimes you need an arm put around you.” O’Brien owes the best part of his life to the group, but creating a world without rules, in his own image, has sparked something uncontainable. “It doesn’t end when you leave the studio,” he adds. “The knock-on effect is like a wildfire. You finish recording and it’s roaring through your life.”

• Earth by EOB is released on 17 April on Capitol Records