Now that you speak of it, maybe it's from the Catilinarian defence that I got this idea. If I remember correctly, Caesar said that killing the men wouldn't be a real punishment since death is the like an eternal sleep. Probably it's here that my contorted mind made a connection with Socrates. In one of Platon's dialogues Socrates is saying that either after death there's some kind of existence (and then he could go and question lots of interesting people) or is nothing but a sleep without dreams.