So there I was happily working away on a piece of code, I clicked the mouse, and the screen on my laptop went blank. It still had power, but it wasn’t displaying anything. Various obvious controls didn’t do anything. Plugging in the external screen from my desktop didn’t do anything. So I rebooted, and it is all fine now. I have no idea what happened. But I think I’ll go have lunch and a walk while I calm down.