nightmares and supplements

Ever since I was little, I have remembered many dreams. Most of the ones I remember best are nightmares. I think I have had a few somewhat 'lucid' moments in dreams, in which I became aware I was having a dream (usually a nightmare) and I am able to force myself awake. I also suffer from insomnia, and i am an extremely light sleeper... the slightest sign of light or noise could cause a stir in me.

Anyways, I started learning about lucid dreaming recently and have started the methods posted on this site... mainly with the dream journal, mental notes, and just now starting to take supplements. I used to take melatonin to help me sleep, but I remember experiencing very vivid nightmares half the times I did it. I took some B6 tonight (200mg) and i am afraid that this may enhance my nightmares or make them occur more often??

Can anyone suggest ways to prevent nightmares or if taking supplements has any affect on this at all?