There's no more ridiculed genre in the literary canon – and you can see why. Most self-help books are written by Americans of the most sentimental and unctuous sort. They promise their readers eternal life, untold riches and an escape from every grubby aspect of being human, all within 300 pages of upbeat, relentlessly repetitive and patronising prose. No wonder the unstated assumption of the cultural elite is that really only stupid people read them.

What terrified me was the prospect I’d permanently upset up my neuro-chemical balance with drugs. My friends and I had messed around with LSD and Ecstasy, and had some good times, but I’d seen friends get badly hurt and sent to mental homes. If my own depression and panic attacks were neuro-chemically determined, then perhaps there was nothing I could do about it, other than take different drugs for the rest of my life.

Probably after a second or two of blankness a thought will pop up.

Then another.

And another.

Suddenly you’re thinking again.

Our brains seem desperate to keep themselves busy. So much so that neuroscientists have defined a network of brain regions that spring into action whenever our attention lapses. They have dubbed this the Default Network. Its activity is so pronounced that our brains burn 20 times as much energy when our mind wanders as they do when we are focussing on a particular task, such as reading this post.