What is depression? You asked Google – here's the answer | David Shariatmadari

Every day, millions of internet users ask Google life's most difficult questions, big and small. Our writers answer some of the commonest queries

To illustrate how horrible it was, being in jail in a wheelchair with four broken limbs after the car accident that prompted me to get sober ... was much, much easier and less painful.

Comedian Rob Delaney's description of severe depression is enough to stop you in your tracks. How can a mental illness, a disorder of thought and emotion, feel so much worse than the most intense physical discomfort? And yet it's not unusual to read about metaphorical bouts between illnesses in which the black dog always wins. "It's a piece of cake in comparison with depression," said Majella O'Donnell, of breast cancer. Even in the realm of mental anguish, it pummels all competitors into submission. Lewis Wolpert found it "more terrible even than watching my wife die". A pain worse than fractured bones, cancer and grief. What is this state, which around 10% of us can expect to experience at least once in our lives? Where does it come from, and what can be done about it?