Melatonin works great for me as well. I take 5mg. Not sure if my dreams are any more vivid than without it, as I've been taking it every night for years. I think I've always had vivid dreams, though I no longer get recurring nightmares (which I had years prior to taking melatonin; not sure when they ended).
I definitely think that if you're taking them under the tongue the doses they sell them in are much too high. Probably make more sense if you're swallowing them.
edit: since everybody is asking the same question about habit forming. I am just passing on the information that I got from my doctor. She made this suggestion to me, and it was beneficial to me. Once I had started using melatonin, I would have trouble falling asleep without it. Valarian root didn't cause that issue for me.