I had to stop metoprolol (50 mg/day) recently as preparation for autonomic testing. I definitely felt it. My heart rate increased dramatically and the pounding sensation kept me awake all night. It's important to say, though, that I was diagnosed with POTS (postural orthostatic tachycardia syndrome), and that may be why I had such a dramatic reaction to suddenly stopping the metoprolol. With POTS I really need a medication to slow my heart down. It sounds from the comments here like the reaction to stopping all at once has been really variable for people, and I'm sure that it may depend on whatever underlying condition the person was taking it for. When I have decreased the dose in past years, I always just tapered down slowly. My cardiologist didn't feel it was necessary to taper, but she also had no problem with my doing the dose reduction gradually.