It sounds more like a reaction to the valium. That means that you need to tell this to your physician and that you shouldn't receive any in the future. It might also mean that you are allergic to other similar medications in the class called "benzodiazepines," of which valium is one. Others are klonopin/clonazepam and ativan/lorazepam. You could also be sensitive to verzed, which is used for brief anesthesia in cases such as flex sig and colonoscopies
(btw, verzed would have been better than valium, as valium often takes more than 1.5 hours to work)
now, if you have had any of the above before (likely, if you are on methadone) and didn't have any reaction, or if you are on them right now without problems, then they likely gave you to high a dose at the clinic and that could be what gave you the chills.