A boy at my son's school was stabbed the other day. Not at school, or near school, or even in this part of London. But it's made me even more nervous than usual.
Every Friday and Saturday night, I hold my breath, hoping my 18-year-old is going to stretch himself out on the sofa and watch rubbish TV. He never does, of course. He's always going out somewhere.
That means I sit there all night fighting visions of him lying in the gutter, bloody and concussed.
'You shouldn't worry so much,' he says.
He's right. Worrying is a completely pointless activity. I know that working myself into a state of hysterical panic doesn't help to keep him safe. (It's like hyper-ventilating on a plane. How does getting faint and dizzy stop you hurtling to the ground?)
'Text me every so often,' I say, as he leaves the house. 'Just so I know you're all right.'
It doesn't help.
He texts me at 11.30pm to tell me he's on his way home. But instead of thinking, 'He's safe! He's safe!', I think, but what if you're mugged at 11.35pm? There I am, imagining you dozing on the bus - and in fact you're being sewn back together in A&E.
If I do stagger off to bed, I lie there clutching my mobile in case he's in trouble and texts me for help. (Which, of course, is exactly what you'd do if you were surrounded by a gang with knives. 'Hold on a second - just got to text my Mum.')
He can't do anything about these mad maternal imaginings. But I have asked him to be a little more careful about the texts he sends.
'Coming back,' he said the other day. And then - oh joy! - 'Not dead yet.'
Not funny. Not funny. NOT FUNNY.