One night about five years ago, just before bed, I saw a tweet from a friend announcing how delighted he was to have been shortlisted for a journalism award. I felt my head spin, my teeth clench and my chest tighten. I did not sleep until the morning.
Another five years or so before that, when I was at university, I was scrolling through the Facebook photos of someone on my course whom I vaguely knew. As I clicked on the pictures of her out clubbing with friends, drunkenly laughing, I felt my mood sink so fast I had to sit back in my chair. I seemed to stop breathing.
I have thought about why these memories still haunt me from time to time - why they have not been forgotten along with most other day-to-day interactions I have had on social media - and I think it is because, in my 32 years, those are the most powerful and painful moments of envy I have experienced. I had not even entered that journalism competition, and I have never once been clubbing and enjoyed it, but as I read that tweet and as I scrolled through those photographs, I so desperately wanted what those people had that it left me as winded as if I had been punched in the stomach.
We live in the age of envy. Career envy, kitchen envy, children envy, food envy, upper arm envy, holiday envy. You name it, there's an envy for it. Human beings have always felt what Aristotle defined in the fourth century BC as pain at the sight of another's good fortune, stirred by "those who have what we ought to have".
But with the advent of social media, says Ethan Kross, professor of psychology at the University of Michigan who studies the impact of Facebook on our wellbeing, "envy is being taken to an extreme". We are constantly bombarded by "Photoshopped lives", he says, "and that exerts a toll on us the likes of which we have never experienced in the history of our species. And it is not particularly pleasant."