Why doesn't my watch self-wind when I'm ill?

Ginny - Automatic wrist watches are really, really clever. So, you used to have to wind a watch because a watch needs energy in order to move the hands around. So, you used to have to wind up a little rotor inside that then drives the hands around. But what these kind of automatic watches have is there's a weighted bit inside that moves every time you move your arm. And you move your arm quite a lot during the day without even noticing it. So, that movement winds the spring that drives the hands. Watches vary in how much energy they can store. Most of them actually, you can take off over night or even if you leave them on, you're not moving over night and they'll store enough energy to still work perfectly well the next day. So, the only thing I can think here is that if you've been ill, you're probably not moving around as much. If you've got flu, you might be taking it a bit easy on the sofa. So, even if your watch is on, chances are, you're not moving your arms around quite as much. So, maybe if you're ill for a day, then it's gone a night and a day, and another night without much winding, that might be enough for it to stop.