A ghostly, grey rubbery screen bulges with indistinct, yet recognisably human, shapes: a hand here, a face there. An unsettling hum underlies eerie, dislocated sounds. An icy voice half sings: “Is there anybody out there?” There is a harrowing howl, then a moment of respite: the word “yes” appears, followed by: “The Samaritans”.

These 55 seconds of existential desperation followed by five seconds of hope were shown on ITV in 1986, when I was seven. This advert had an effect on me. It was as if I had suddenly become aware of the extent to which humans could suffer. I had no idea what the Samaritans did, just that they were there.

It is difficult to explain why, 33 years later, I have ended up a Samaritan. I only know it was something I needed to do. I live a mercifully uncomplicated life, and was aware I could drift into a beige middle age; I could see years of pleasant purposelessness opening out before me. Something new had to happen and I had no doubt that thing had to be volunteering for Samaritans.

As to what this would entail, I was rather clueless. Still, I was impressed by what I knew of the charity, so in January last year, I went to an event for potential volunteers at my local branch in Coventry. It was powerful stuff: they respond to a call for help every six seconds, answering more than 5m calls a year. It also became clear that Samaritans are engaged, empathic and available whenever they are needed by a caller: they do not operate to scripts or algorithms. I got through the selection process and began training.

My fellow trainees were a diverse bunch, from all sorts of backgrounds, living in all sorts of circumstances; there was as much to learn from them as from the training team. Then, after three months of intense and intensive sessions, it was time to take my first call.

When that phone rings, there is no telling what awaits. The call may last a couple of minutes or several hours. The caller may be of any age, race or class, from any place. They may be in a state of panic or profound anxiety; they may have had to face a lifetime of problems alone; they may feel suicidal. What becomes immediately clear on your first shift is that there is a vast tide of human anguish, much of it hidden in unvisited homes, masked by watery smiles, sequestered in double lives.

Samaritans offers a potent blend of anonymity and humanity: the volunteer cannot see the caller’s number or location, and has no way of identifying them beyond what they are willing to disclose. Samaritans don’t try to cheer up callers or promise everything will turn out for the best; rather, they tend to say as little as possible, giving callers what they often lack: space and time.

At first, I was terrified of saying the wrong thing. But as the weeks passed, I found the more I relaxed into it, the more use I could be. Aside from helping others, the change in me was pronounced: rather than try to drown any negative emotions I might experience, I was fully feeling them and naming them. The frustration and anger we all feel, but which I had previously tried to suppress, were replaced with a new emotional candour. It has been unsettling and destabilising in the best possible ways, a strenuous but invaluable workout for the soul. Thanks to Samaritans, I have overcome my fear of middle age.

Life exists in beautiful and sometimes bewildering diversity, and one encounters a vast spectrum of this as a Samaritan. But what has become ever clearer to me is a deep commonality. I have long appreciated that we all experience fear, anxiety and despair; but this is a truth that hits a Samaritan in the heart. We are all emotional beings trying to get through life, and sometimes we mess up or other people mess us up. And Samaritans’ research shows how decisions taken by those in power can have devastating effects on the lives of vulnerable people.

Volunteering is a commitment in time and emotion, but it has brought to my life colours that I did not know existed. Samaritans has done much work to soften its image since those stark 80s adverts; it wants to reach more people before they come to that point of utter helplessness. It is keen to show it has a human face, too – which is partly why I’m writing under my own name. But its lifesaving work continues just the same. To be listened to can help to bring great healing. What a privilege, then, to be the listener.

• Samaritans has launched a campaign sharing the stories of men who have come through tough times. Visit Real People, Real Stories for details. In the UK, Samaritans can be contacted 24 hours a day on 116 123 or by emailing jo@samaritans.org