For the irony of this ho ho ho happy time of year is that depression is all about. The festive season is a lacerating time for those who cannot claim good relations with their families, or have some kind of issue going on. And who among us cannot claim some kind of issue?

Merely among my immediate circle I can count: cancer, divorce, death, childhood illness and dementia. Or maybe there is none of the above, yet still gloom descends. Either way, some will find it difficult to cope. I know, because I have been one of them.

A natural introvert, I have learnt to give every appearance of openness, personally and professionally. Nevertheless, the fact I struggle with my mood to the point at which I am medicated for it is something I have chosen to conceal.

As the daughter and, indeed, granddaughter of a psychiatrist, you might imagine I would be more open about such matters. And, certainly, I see no stigma in other people's wretchedness. Only in oneself does one perceive misery as failure.

No workmates and few friends have ever suspected that I harbour such inclinations, so concerted is my air of sprezzatura. A colleague once informed me that I was "like a swan, gliding about, beautifully unruffled", and how I prided myself on the description. Alas, my Odette conceals an Odile.

Even as a child, I was pretty miserable: watchful, adult, with none of the ease other infants enjoyed. My father would remark upon my "mercurial" nature. I was all or nothing, elated or distraught, devoid of the happy banality of middle ground; glass not so much half empty as fractured into shards.

As an adult, I remain mercurial, beyond which there have been entirely logical reasons why the negative might take hold.

After a period in my early 30s in which first I was seriously ill, then my father dangerously so, my mother refused to speak to me for eight years, for reasons I had very little to do with. She encouraged my siblings to follow suit and some of these relationships remain strained.

There is a family history of anxiety and addictive behaviour. I live and work alone. I was single. I drank too much. I barely slept. When I did, I was beset by savage nightmares, infecting each morning with a psychotic pall.

The first time I was hit by depression proper was a year into my mother's disowning. As the 12-month mark arrived, it occurred to me that this could be forever, and up I slowly seized. Full paralysis took place in the King's Road branch of Marks & Spencer in London, I felt as if I could no longer put one foot in front of the other.

My doctor prescribed psychotherapy, which I did for several months until I ran out of money. It was incredibly hard work – after the first session, I vomited – but it succeeded, providing me with a safety net of self-knowledge that I continue to draw upon a decade on, not least when my mother died in June.

The intervening years were not all sweetness and light. However, the next great descent came in my late 30s, an angst that went past angst and terrified me that I wouldn't be able to support myself. This time I was put on the antidepressant Citalopram.

I'm not ashamed of my medication: I see it as a vitamin that brings me up to everybody else's level. My worry that I would stop being myself on it and "go Stepford" has not – alas – materialised, and I still succumb to unhappiness. I was never actively suicidal – one has to have drive to take one's own life, and I had none.

However, the drug changed my mental loop from "I want to die" to "things could be worse". Only if one has been there will one appreciate the enormity of this achievement.

I am a complete advocate of medication. And, yet, even as I type the word "Citalopram", I start to weep, such an admission of weakness does it feel – weakness that one can't buck up, pull oneself together, carry on. It remains a paradox that, although you have to be incredibly strong to handle depression, the way it manifests is as frailty: a frailty that begins in the mind before swallowing its host whole.

For some reason – or no reason – you start feeling flat. Flat turns to low, low to paralysis. There is lethargy, a loss of outside interest as the tunnel vision takes hold. You stop washing. Your appetite will be ravenous, or void. Just at the point at which you most need human contact, you will be repulsed by it, settling into a leaden isolation. You may not want to take your life, but your life will have ceased.

At this stage, it is impossible to simply pull oneself together, and any desire to keep soldiering on isn't going to march you back to health.

Moreover, despite the isolating nature of the condition, this is something that ever more of us are learning. bout 20 per cent of adult Australians are affected by mental illness every year and quarter of Britons will experience some kind of mental illness, with combined depression and anxiety the most common disorder.

There are steps that one can take, not just the drugs – although the drugs can be crucial – but what is known as "self care". Think not merely "sleep hygiene", but "life hygiene": nourishing oneself, cutting out the depressant that is booze, fixing one's sleep, movement and/or exercise, ensuring one gets a regular dose of daylight.

Some people swear by the efficacy of cognitive behaviour therapy. My experience was that it was therapy for thick people, but I know others for whom it has been life-changing. Meditation has proven form. A balance must be struck between being kind to oneself versus being disciplined (the odd duvet day is fine, complete self-ostracism isn't).

Such strategies are never more relevant than during the so-called festive season, an enforced frivolity not helped by everyone and their dog asking you what you are "doing for it" from October 1 onwards.

I used to reel at the fact that people could be so cavalier. An editor once called on Christmas Day to ask if I knew anyone who could be a case study for suicidal singles.

Another time, I phoned the Samaritans, only to be told that I was too posh to have problems and to get off the line.

Meanwhile, you're only as sick as the secrets you keep, or so the bumper sticker goes. And, thus – finally – I'm facing my fear: this thing of darkness I acknowledge mine.

The Daily Telegraph