Good question. And there’s no easy answer.

Some illnesses – like anaemia or diabetes – can be ‘proved’ with a blood test. Not so depression, which means it’s diagnosed subjectively - a process aggravated by the fact that its symptoms, in mild form, blur with the normal day to day pissed offness that we all experience.

Having said that, there are some features which are pretty characteristic. Such as a persistent low mood, lasting at least some weeks, which won’t necessarily be explained by personal circumstances.

This may manifest itself by anything from mild tearfulness through to thoughts of suicide. Typically, men will interpret, or dress up, their depressive symptoms as general malaise or tiredness – a distortion which can mislead friends, family and even doctors.

Other pointers include poor sleep, irritability, memory problems and lack of concentration. Loss of sex drive or erectile dysfunction may feature, too. And the situation may be complicated by unhealthy spin off such as alcohol or drug abuse.

As for when all this becomes ‘clinical depression’, perhaps the most pragmatic answer would be to say when it becomes a real problem, affecting your normal daily functioning – or when those around you point it out.

If self help measures such as stress busting, problem solving, a lifestyle shake up and therapeutic exercise don’t improve matters, it’s time to speak to your doc – pronto if you’re feeling suicidal.