Content warning: This post contains details of depression may be triggering for some readers.

My grandfather has always struggled with happiness.

There have been times when he has felt overwhelmed by sadness, and others where he has been sick with worry. For decades he has been plagued by a sense of guilt and unease. He is perpetually worried about his health, despite the fact he eats very well, exercises plenty, and there is absolutely nothing wrong with him.

My grandfather is incredibly intelligent and interesting, yet has always been extremely hard on himself. There have been times when he has been completely crippled by self loathing and anxiety.

But, up until recently, he had never talked about any of that.

About a year ago I came across a book titled Darkness Visible by William Styron. I saw it recommended online with a few excerpts and was struck by just how eloquently it described the experience of depression.

I read it in a day. And as soon as I closed the last page, I called my grandfather.

Next time I saw him, I gave him the book. I figured he would probably nod politely, and then add it to a pile of "oh, yes...I'll read that" books he had accepted from insistent relatives.

But the next day I got a phone call.

He'd gone to the GP, and plonked the book down in front of him. After decades of doctor visits, for the first time he was able to say "this is what I have... explained better than I ever could."

Mia Freedman on why routine is anxiety’s best friend. (Post continues after audio.)

That is the power of a book.

They can change lives, or provide a vocabulary for a particular kind of experience that was previously unexplainable. They can also powerfully remind us that we're never really alone.

So to anyone who wants to better understand mental illness, or is struggling with their own, here are the books you absolutely must read.

1. Darkness Visible by William Styron.

Styron's Darkness Visible charts his descent into depression and his eventual recovery. He writes with searing honesty, and was prompted to tell his story of "despair beyond despair" after the suicide of Holocaust survivor Primo Levi. Darkness Visible emerged out of an article Styron wrote for Vanity Fair, where he argued that "the pain of severe depression is quite unimaginable to those who have not suffered it."

The following is an excerpt from his book.

In depression this faith in deliverance, in ultimate restoration, is absent. The pain is unrelenting, and what makes the condition intolerable is the foreknowledge that no remedy will come — not in a day, an hour, a month, or a minute. If there is mild relief, one knows that it is only temporary; more pain will follow. It is hopelessness even more than pain that crushes the soul. So the decision-making of daily life involves not, as in normal affairs, shifting from one annoying situation to another less annoying — or from discomfort to relative comfort, or from boredom to activity — but moving from pain to pain. One does not abandon, even briefly, one's bed of nails, but is attached to it wherever one goes. (Post continues after gallery.)

2. The Bell Jar by Sylvia Plath.

 3. Man's Search for Meaning by Viktor Frankl.

Every person I've spoken to who has read Man's Search for Meaning, says that the book changed their life. It is the perfect book for anyone struggling to find meaning or grappling with feelings of hopelessness.

Frankl was an Austrian Jew imprisoned by the Nazi's during World War II. After his release from Aushwitz Concentration Camp in 1945, he set out to write Man's Search for Meaning which is part memoir, part analysis. It took him a total of nine days.

Since reading it, I hear it mentioned all the time. Recently, Chris Martin from Coldplay was interviewed about his marriage break up from Gwenyth Paltrow. Usually a man of very few words, he reflected that during one of the lowest times in his life, Man's Search For Meaning helped pull him out from the abyss.

The central argument of the book  is “suffering ceases to be suffering at the moment it finds a meaning". Coming from a man who endured such violence and despair, Frankl's work carries a profound air of authority. Anyone in the midst of an existential crisis can draw on his unparalleled wisdom; “Those who have a 'why' to live, can bear with almost any 'how'.”

4. The Noonday Demon: An Atlas of Depression, by Andrew Solomon.

Andrew Solomon's The Noonday Demon is one of the most cited modern texts when it comes to depression.

His Ted Talk 'Depression, the secret we share', has been viewed almost six million times, and explains anxiety and depression in a poetic and eye-opening way.

The Noonday Demon was published in 2000, and as well as exploring his own struggle with mental illness, Solomon interviews sufferers, doctors, politicians, philosophers and scientists in order to reveal the "subtleties, the complexities and the agony of the disease."

His book challenges readers to re-examine the way they look at the world, and redefine how they understand the human condition. He speaks on behalf of those currently suffering, because, in Solomon's words, “Depressed people cannot lead a revolution because depressed people can barely manage to get out of bed and put on their shoes and socks.”