because you napped.
is there something about the statement DO NOT NAP that you fail to understand? don't nap, be tired for one afternoon of one day, suck it up and get a great night's sleep.
Sorry, but this is terribly simplistic. Napping does not cause insomnia! When I've been afflicted with bad insomnia, I cannot nap during the day, no matter how exhausted I may be -- and I still don't sleep the next night. After a few days like this you begin to feel like a zombie. The frustration become intense. If napping truly is an option, then you are probably not such a hard case.
Melatonin is not a panacea, particularly since you don't know how much is actually in any given supplement, but it has occasionally seem to help me at least reset my circadian rhythm when switching time zones frequently. I find that 8 hours before bedtime is about the right time window, which is why I suggested ~midday. (As I'd probably want to try to go to bed around 9 so I could actually get 9 hours of sleep and still get up at 6). I'm usually up much later, but not when my sleep quality has been poor.
FWIW melatonin certainly doesn't "put you to sleep" in any way, for me at least it seems to just help to take the edge off and lets me get to sleep even when my body would otherwise not be ready to do so, as in the case of being thrust in a new time zone every other day.
I also find that total darkness (i.e. not even any LED alarm clocks) and some optional white noise help me too, but I don't suffer from extreme insomnia.
You turn in early! I know, melatonin does seem to help for some people. I find it does make me a bit drowsier, but that it does little or nothing to help when insomnia strikes. Even the antihistamine sleep aids are ineffective, and they make you truly wobbly (well into the next day). Of the pills you can pop, only Lunesta an Ambien actually work for true insomnia.
Total darkness is important and is recommended by sleep experts. Getting the clock out of the bedroom is useful too. I had one of those clocks that projects the time on the bedroom ceiling. This is the insomniacs worst nightmare, so to speak! I also stopped our grandfather clock. As much as I like the sound during the day, when I started to have problems sleeping, it was driving me nuts hearing the hours chime away. The weird part is, it never bothered me before.
Insomnia is a very bizarre and deeply frustrating condition. People who've never had it just don't know. Before I experienced it, I certainly didn't. So when somebody says, "skip the nap and you'll be fine," I just have to laugh.