10 years is an awful long time to be on Toprol or any beta blocker at your age and some of what you describe may very well be side effects of long-term Toprol usage. An experienced electrophysiologist would probably do a better managing your medications or even the need for them.
Experimentation with the various anti-arrhythmics and strengths available carries a risk, and perhaps your physician doesn't want to head down that path with you. Metoprolol is a beta blocker that is usually well tolerated by most, and perhaps this is why he prescribed it for you. 150mg alone can definitely slow you down, and a dose of that strength can also slowly build beyond the therapeutic level that your doctor intended ypu to be on. I had been on strengths as high as 200mg. andd you do I deed feel like a zombie with that much in you.
At your age, you owe it to yourself to find a resolution. If your physician is reluctant to try a different drug therapy, I think you should search for someone who will.