I had a panic attack once in the bathroom of a Wimpy. It is a long story involving a motorway, a vicarage and, oddly enough, a pig – although not in the David Cameron sense. But the relevant portion involved me sitting on the floor of the burger joint’s bathroom, hyperventilating, which felt like I couldn’t breathe, while being aware that too much oxygen was entering my body. It was a horrible, confusing sensation, and I didn’t want fries with that. I try not to think about it as my breathing coach explains that, for the next hour, I will be doing something akin to this, in the interest of therapy.

London-based Breathpod (breathpod.me; £150 for up to two hours) offers group or one-to-one breathing workshops. This sounds about as necessary as going on YouTube to learn the difference between left and right. I feel more intrigued when I meet my coach, Stuart Sandeman, who looks genuinely beatific, a Scottish Zac Efron – perhaps because I have been seeing posters everywhere for Extremely Wicked, Shockingly Evil and Vile, the film in which Efron plays, er, the serial killer Ted Bundy.

Sandeman, the founder of Breathpod, does a lot of functional work in which his clients relearn natural movements they have forgotten: breathing from their belly, not their chest; through the nose, rather than their mouth. But it turns out my natural pattern is, apparently, pretty good. Of course it is – I have been breathing since before he was born.

Another strand of Sandeman’s work is hypoxic training for performance, which involves working out in oxygen-limited conditions, replicating the effects of high-altitude acclimatisation. I get a nosebleed if I see a watercolour of the Alps on Antiques Roadshow, so thankfully we are not doing that today. Instead, we focus on a third, supposedly therapeutic aspect: breathwork. I have had a fair bit of anxiety of late and I reckon I would benefit from a touch of relaxing breathing. However, it turns out that is not what this is, either.

Most of us intuit a relationship between breath and feeling. Think about the rapid shallows of anxiety, panting of lust, the deep draw of the contented. When our emotional state changes, our breath changes. Ancient practices such as yoga describe this as a feedback loop, which runs both ways. Change our breath, change our feeling. (“It’s a biohack,” Sandeman explains, which sends a Bundy-chill through me.)

Lying propped on some blocks, wrapped in a blanket, I breathe in slowly, fully, then drop the breath quickly, without effort, and start again. This is the almost-hyperventilation part, although it is not stressful. I am altering the balance of oxygen and carbon dioxide in my blood, with Sandeman murmuring affirmations and encouragement to let things go. He presses me, quite hard, in my abdomen. With wave after wave of breath, I start to feel things, including a buzzing in my lips, arms and stomach. Every so often, he has me stamp my arms and feet and throw my head from side to side, like a child having a tantrum. Lucky I have no dignity or I would have lost it at this point.

In fact, I do lose it. After an hour, tears come wracking up through me – submerged grief and pain and helplessness. I do feel – oh God – as though I am in my heart centre. I release my anxiety in gulping sobs. I weep for a friend who is very unwell, whom I don’t know how to help. It isn’t all traumatic – I also arrive at benign clarity about unresolved issues I have been pushing away.

Sandeman later confirms that this is common. In his corporate work, clients often come to the realisation that they need to leave their jobs – something of an own goal for a team-building day. Or maybe not.

I can’t share much else, as it feels intensely personal, but the business should surely be renamed Catharsis R Us. By the time I become aware of the sound of singing bowls and the light foot massage I am receiving, my mind is completely still. Whatever the physiological mechanism at play here – affective breathing is still little understood – it is powerful. My morning’s anxiety has been replaced with an energised calm, which may make no sense, but I am too chilled out to care. This “breathing” thing is an inspiration. I think I will stick with it for the rest of my life.

Any downsides? The prop used to keep my jaw open gave me dry mouth.

Wellness or hellness? Extremely wicked. I feel shockingly peaceful and alive. 5/5

• This article was amended on 15 May 2019. An earlier version said that one of the natural movements Breathpod helps its clients relearn, was breathing from their chest, not their belly. This has been corrected to say breathing from their belly, not their chest.