Toprol-XL and atenol

When I first ever started on beta blockers for my heart control, I was completely taken by surprise at the side effects. I started on atenol(sp?) and it really knocked me for a loop. I got so tired I could barely move or get out of bed. All I did was lay around with no energy what so ever. I felt dizzy on many occasions and had no appetite. After I think 3 or 4 days, I started feeling better.......( Now that I am on Toprol and have read the instructions about "use caution when first taking this pill until your system gets used to it", I have a much greater appreciation for this warning.
My Dr has informed me that these beta blockers stay in your system for 3 days or so (I once forgot to take my meds for 3 days in a row). I agree with that because on the beginning of day 4 my heart would race uncontrollably which it never did when I was steadily on my meds....