I have fibromyalgia too, and have been on a kajillion drugs over the last 15 years attempting to get a reasonable night's sleep. The best combo I ever took was klonopin and serzone, but serzone was taken off the market about a year ago. The generic is still available, but I figure if the drug has been "black labeled" by the FDA, I probably don't want to take it
I took Sonesta for a while and had all the problems you are describing. Now I just take klonopin. Doesn't work as well, but not as many side effects.
The metallic taste is "dry mouth". It's a common side effect of a lot of drugs- your salivary glands are not fully functioning. You may also have dry, itchy eyes but not always. Some of the ways I've found to combat dry mouth are to add a few drops of lemon juice to my water bottle and sip all day. The lemon makes you salivate more. Also, there is a toothpaste, mouthwash and gum made by
Biotene which are really helpful. Most drug stores and large groceries carry it. Regular toothpaste and mouthwash have alcohol in them which dry out your tissues...not what you want to do!
Combatting dry mouth is important because saliva is what helps fight bacteria in your mouth. Without it, you'll have excessive plaque buildup, gum disease, and tooth dcay. Floss and extra cleaning are your friend if you have to stay on a med which causes it!
Mel