I occasionally take melatonin for sleeplessness, especially if I've had some kind of stressful event which makes me lie awake brooding. I buy the small dose (1mg) pills and will swallow between 1 and 3 of those depending on how wired I feel. Well last week I had a pretty bad time of it with work related stress so I started taking 3 pills per night, soaring to an unprecedented 4 on one occasion. Yeah 4mg should do it. 

Well the day after the first dose, I had this horrible dull headache all day and felt sort of like a stuffed parrot with the sawdust leaking out of it (to borrow from Wodehouse). I put this down to the stress. Day 2 and the headache continued. Felt a bit nauseous as well. Day 3 and the headache was still there. I started to get a bit worried. It crossed my mind that perhaps it was a reaction to a change in air pressure or humidity or something (it's starting to get warm & sticky here in NYC). Day 4 and enough was enough. I was like a freaking zombie. Well that night I reached for my melatonin again because I felt sure the stinking headache was going to result in more sleepless brooding. And taking a closer look at the label, I noticed that instead of buying my usual 1mg dose I'd actually bought 5mg pills. I'd been doped up to the freaking eyeballs on the stuff! 15mg a night instead of 3mg. Doing some research I discovered that sure enough, large doses of melatonin can cause dull headaches and nausea the next day. So I quit taking it altogether and today, lo and behold, no headache whatsoever, back to my normal self. 
 
I have to take more notice of what I'm putting in my basket at the supermarket 

I have some on the shelf but I never tried it.
 
I had sleep issues for the longest time but I just thought it was normal for my own messed up self. It'd either take me hours to fall asleep or then I'd sleep and hour or two and wake up and sat awake for a couple of hours.
 
But ever since I cut coffee back - only 2 in the morning, and then tea and herbal tea for the rest of the day, I have no problem falling asleep and saying asleep.
 
I do think that Melatonin could be useful the next time we plan to take the plane - I usually start having trouble sleeping days ahead... But then, considering the nightmares, maybe I'd rather stay awake. That way, I've exhausted all the anxiety reserves that I had before I even board the plane.

I used to have the most awful trouble getting to sleep every night until I realized that it was the bright blue light of my computer monitor screwing with my sleep cycle. I'd stay up until 1-2am every night staring at the thing and then wonder why my eyes kept popping open when I went to bed. I realized this when I installed Flux, the free app which warms and dims your screen colors in the evening. It really works. I also removed all of the bright "natural light" bulbs I had in my apartment and replaced them with with soft yellow light. No more trying to create daytime light conditions in my apartment at night when I should be winding down. Everything's mellow in here now and I have much less trouble sleeping, apart from when I have something on my mind genuinely worth lying awake over. 
 
I didn't notice any nightmares with melatonin, then again I have a pretty high threshold for what I'd consider a nightmare. I have some pretty wacky dreams and I always enjoy them no matter how weird they get. A nice hit of ginkgo biloba before bedtime is a sure fire way to induce those epic movie plot ones. 
 
Oh and bananas are a great way of getting to sleep. Lots and lots of bananas. 

I saw one being advertised that has a nice mix of melatonin, valerian root and tryptophan.  If that doesn't make you relax and fall asleep, then you might as well just stay up!

I've tried valerian root, it makes me feel like crap the next day.

I seem to fall asleep even faster since I've started drinking herbal tea. At first I only wanted to try it to see if it could be help w/ congestion, provide some sort of relief - and it does, at least a bit. But, whether it's because of the hot beverage or whether it's psychological or whatever, usually, after a cup, it doesn't take long before I really need to sleep.

I stopped coffee about a year ago and I think it's helped a lot. I still drink a lot of green tea though. Recently I've fitted addicted to matcha tea. It's supposed to be insanely healthy although I'm reluctant to buy any Japanese grown brands since the nuclear accident. Dandelion tea is great as well.

sharke
... I'm reluctant to buy any Japanese grown brands since the nuclear accident. ...

Oh come on!  The glow-in-the-dark side effect makes you very popular at parties!