I have recently started to use a chlorhexidine mouth wash for my gums. after the first use, i woke up with a very bitter taste in my mouth. is it normal? how long does the bitterness last?

I trust you didn't use more than the recommended amount. There may be some bitter after taste,especially if you rinse your mouth out with water right after using it. If the after taste doesn't clear up soon after rereinsing your mouth out in the morning, I suggest switching to another pleasant tasting,alcohol free,mouth wash.

If your Dentist prescribed clhlorhexidine (s)he must also have given you specific directions for use. If not, call and ask for directions.