Is it normal to have nightmares before your wedding?

I can't sleep, I keep having nightmares of all the terrible things that can go wrong will go wrong at my wedding in a month, I'm losing weight and I have black bags under my eyes. My fiance tells me everything is going to be Okay, but I still can't get out of my head the impending disaster, because I KNOW something will go wrong I have such awful luck at things like this. How can I calm my nerves and get some sleep so i don't look like the bride of Frankenstein at my wedding?