The woman on the bus, years ago, was crying. I sat down beside her; it was the only vacant seat left. - "I'm sorry," she said. "I don't know why I'm crying. I'm not sad." - "My guess is you're not getting much sleep." - "You're right. How did you know?" she asked. - "Lack of sleep is the main reason people find themselves crying," I said. "They can't help it. It's a physical thing, not emotional. Don't let them tell you you're depressed."