One of the biggest obstacles to people getting treatment for depression is stigma. Because many people still feel ashamed of suffering from depression, they are reluctant to admit they have it. They don’t – or won’t – talk about it.

Now, if you break your arm, your friends and family will sympathise with you and, in my day, they would sign your cast. Tell them you are depressed, and you get comments like: “Snap out of it,” “Go for a walk,” or “Cheer up.”

If your teeth give you trouble, you go to a dentist. If you feel ill, you go to your GP. But get depressed and stay in bed because you can’t face seeing anyone, and people think you are pathetic or malingering.

Ricky Gervais, the British comedian, says telling someone who is depressed to “perk up and snap out of it” is about as useful as telling someone with cancer to stop having cancer.

But we use the word depression very loosely. We talk about a child who can’t have their birthday party outside because it is raining as being “depressed”. Yet we use the same word to describe a person’s state of mind just before he puts a revolver in his mouth and pulls the trigger.

Now, it used to be thought that serious depression was caused by a chemical imbalance. The jury is currently out, with some schools of psychology saying the evidence doesn’t fully support that position. There may be some chemical imbalance, but, according to them, it may not be the main cause. More and more, it is thought that the imbalance may actually be caused by depression.

There are several theories as to what causes depression. Perhaps one of them might help explain something I have never really got my head around – why celebrities commit suicide.

Robin Williams. Kurt Cobain. Anthony Bourdain, the celebrity chef – I once had a drink with him in New York, although I don’t think that had anything to do with him killing himself. The South African hip-hop artist Riky Rick died by suicide after battling depression. Ernest Hemingway. More recently, golfer Grayson Murray. The list seems endless.

These are people who appeared to have everything most of us aspire to: fame, money, adoring fans, gorgeous partners, extraordinary talent. So what was missing in their lives? What could have made things better?

And what about famous people like Bruce Springsteen, Jim Carrey, JK Rowling, Lady Gaga and Prince Harry — or historical figures such as Winston Churchill and Abraham Lincoln – all of whom have spoken openly about struggles with depression?

The statistics on depression are overwhelming. Worldwide, about 280 million people suffer from depression. When I started writing a book on the subject, at first I kept it to myself. I didn’t want to keep explaining why I was writing it. But then, one night in a pub, I mentioned what I was working on – and everyone within earshot wanted to share their story with me.

At first, I thought they wanted to ask questions. They didn’t. They wanted to tell me their stories.

And virtually everyone I know has something to say about depression. The number of friends I have on antidepressants is astonishing. And when you hear that SADAG (the South African Depression and Anxiety Group) fields more than 3 000 calls a day, you realise how serious it is. Even more startling: one in four of those calls is from a potential suicide.

Another staggering statistic is that more than 700 000 people around the world die by suicide every year – roughly one every 45 seconds. And the number one risk factor for suicide is depression.

Think about suicide for a minute. If I held your head underwater, eventually you would kick, scratch, bite and do anything in your power to get another breath. It would be instinctive. Your body wants to stay alive.

But a person committing suicide effectively holds their own head underwater until they drown.

The paradox is that suicide is a permanent, irreversible solution to what is almost always a temporary problem.

It goes without saying that depression is real – just as real as a gaping wound. But because you can’t see it, many people don’t treat it as a genuine condition. Instead, they see it as a character flaw.

Now, as far as we know, we only have one life. There may well be an afterlife, but that’s a question for another day.

Right now, we are dealing with the one life we know about. And the intriguing thing is that, never mind outside dangers – wars, pandemics, governments, other people, crime, animals, in-laws, or whatever else you fear – the biggest threat to your happiness is your own brain.