Metoprolol Succinate ER and bouts

After I switched to Metoprolol Succinate ER, the generic form of Toprol XL, which I had used for 4 years with no noticeable side effects, I began having the experience of everything moving faster - heart beat, pulse, intestinal peristalsis was highly accelerated. Daily bowel movements increased from one or two normal a day to three or four. After a few weeks this condition was punctuated by brief bouts of diarrhea(not something I am prone to) approximately weekly.

Since nothing else changed in my food, supplement or prescription drug intake, my digestive system has always worked extremely well, without problems; and because I had a colonoscopy showing no abnormalities in recently years and no occult blood in the stool in a recent doctor's visit, I am wondering if the Metoprolol is the cause. My entire system feels like it is on some type of "speed' drug, sort of a mania experience.

Have there been other reports of this with people who switched from Toprol Xl to the generic?