Initially I usually handle it by announcing gloomily that I can no longer write, have never been any good at it, and anything I’ve managed to do so far in the writing business was probably just sheer blind luck anyway.
Then I mope a bit. I drink a lot of tea. Check with Amanda and find out if she’d still love me if I never wrote anything again (she always says yes). Call my agent to apologise because, obviously, she will have to spend the rest of my life and hers getting me out of any existing writing contracts.
And then, after a few days of that, I get interested in something and start writing and get happy, and am usually vaguely surprised when someone mentions how miserable I was a few weeks before."