Metoprolol 25mg symptoms and conditions

I have been taking kelone for 20 yrs due to palpitations and a rapid HR the pappitations got worse over the last few months and I was panicky so I went to the dr and this is what happened!

I was put on metoprolol 25mg 2x's a day and it didn't work. I found myself in the hospital with a rapid HR and not feeling well. I had been on kerlone/betaxolol for more than 20 yrs and my NEW Dr was not familar with it so he swithched me. I went to fill the RX and was told by the PharmD that it had a very short half life compared to my old med. I asked the Dr. he said lets try it. Well like I said I was in the hospital within 2 days. I wanted to know what you all think about switching from generic to Toprol Xl and what should my does be? I was raised to 50mg metoprolol 2x's a day and it still doesn't seem to work. I know it is wearing off and I feel crappy! I am 38 with a hx of type 2 Diabetes which is controlled and I take Metformin 500 mg er. I also take Crestor 20 mg all other things are ok but I can't excercise or do any activity due to the feeling my heart is going to POUND out of my chest.
Any and all advice is welcomed since I am new to this med and dont't know if I go back to the palpitations I had with my old one or feel like crap with the new one.