....that's not the reason for his perpetually sleepy look, which tends to mask his fire-at-will wit. He sometimes stops midconversation to take a pill to counter the effects of narcolepsy. So far it has had little impact on his career, though he says he has on occasion nodded off in his car, as well as in afternoon writers' meetings -- ''not the best way to make people feel good about their material,'' he grants. And he acknowledges that ''Jimmy Kimmel, the narcoleptic late-night host'' has a certain weird, circus-sideshow ring to it.