Not a medication, but I've found that large amounts of sugar puts you to sleep; especially if you're eating it in bed. It heightens your sugar levels, with them plummeting, after a while, causing tiredness. Not too healthy, though; especially not for people who no longer are young.
I'd strongly advise against using Valium or similar drugs; Valium can cause permanent memory loss, when you stop taking it. Imagine waking up to a world you're completely unfamiliar with, one day, just because you stopped taking it, the day before.