I woke every morning from five hours of enriched REM sleep, as wide-eyed and energetic as a hyperactive child, my head spinning with a thousand disintegrating dreams. I wouldn’t so much as yawn until eleven forty-five – but fifteen minutes later, I’d go out like a light. Melatonin was a natural circadian hormone, far safer and more precise in it’s effects than crude stimulants like caffeine or amphetamines (I’d tried caffeine a few times; it made me believe I was focused and energetic, but it turned my judgement to shit. Widespread use of caffeine explained a lot about the twentieth century.)

[Distress by Greg Egan p27]
(of course that isn’t what Greg thinks, it’s a thought he put into the head of one of his characters)