Do you ever suddenly dip into hopeless gloom at five o’clock in the afternoon? For no good reason you can fathom, your energy dies and you survive the hours until sleep with a sense of hopelessness and dread. This happens to me maybe once a quarter and I’ve observed something even stranger: the next morning I rise from bed buoyant and cheerful. It’s as if one extreme state is accompanied by the other. Can I explain it? No, and I’m not sure I want to.