"All sorts of things can keep one awake. But as you get older - this is what the stroke thing really brought home to me - this thing that I never paid attention to: my brain. I've always been conscious that, of course, after a night of getting stoned, my head would feel foggy; if I got drunk the night before I'd be hungover. But that was the extent of my concern about my brain. And then with the stroke thing, it made me realize, "God! That's my main source of income." So it relates actually to your other question about growing old."