I recall when I was drinking the 18-20 cups of coffee per day (these were mugs, not the small actual measurement called a "cup") people would ask: "How do you get to sleep".
For years, the very first thing down my throat every morning was a Vit. C tablet washed down with Pepsi, and the very last thing down my throat at night was Pepsi, and one morning I actually felt a caffeine buzz for the first and only time; for the entire rest of my caffeine abusing life I've never noticed any effect from the caffeine, not even when I've slowed down my intake.