A Strange Phenomenon

This has never happened to me before. My room light won't turn off. I've had lights that won't turn on, in power cuts or if the bulb's gone, but never one that wouldn't turn off. I've put the switch in both positions many times, but nothing. At the moment I've left it in the state I'm confident is 'off' (the same position as the switch for the bathroom light, which did have the decency to turn off); I'm not sure if that's a bad idea as the off position is obviously broken so maybe using it is not good? or whether it's the right thing to do as then it may correct itself at some point whereas if I leave it in the on position it will have to use energy all night.

At least I don't have problems sleeping with lights on. I'm not going to bother some poor on-duty staff member at 3am!