Aside from medical issues, the beguiling effect of letter-writing is the only thing that the former mayor is losing sleep over.

Question: What keeps you up at night?

Ed Koch: No. I don't -- there are a couple of nights that I am sleepless, but I think that's more medical than anything else. Certainly not because I'm worried; but I do get up at night. I keep a pad on my night table and my mind, like the minds of most people, functions 24 hours a day and your mind is working out solutions to problems that confront you in the course of the day and suddenly you are aware of the fact that a phrase you’ve been thinking of to add to one of your letters – I love writing letters, is perfect and you just thought of it and you know that you won't remember it when you wake up. So, you fight yourself awake, that's at least what I do because the body doesn't want to get up, it wants to sleep. And it beguiles you, and it says, "you'll remember it in the morning." And my response to it always is, "No, I won't." And I fight until I open my eyes. And then I write the phrase down, and then I go to sleep.