Toprol-XL and sleep last night

I just started Toprol XL on Friday (four full days ago). I was put on it to decrease heart rate and palps, I have Inappropriate Sinus Tachycardia. I am 35 years old. I was prescribed to take 50mg twice a day, and I am on the generic. Almost immediately, stomach upset started with diarrhea. I still had some palps at 25 mg. twice a day, which the MD told me to start with for about two days. So, after doing the 25mg for two days twice daily, I went on to the 50mg twice daily. Last night I slept for twelve hours straight, and then felt like I had a sedative after I got up. After taking my next 50mg dose this morning, I got so sleepy again, and felt like sleeping and was in a fog after the twelve hours of sleep last night! I can't imagine mixing anything else with it that causes drowsiness, you would pass out. I feel like I can't think clearly,and feel more crabby and irritable. I called the MD this am. and was told to go back to 25mg twice a day, and that side effects would lessen over time. I have had this sinus tachycardia problem for years, and got diagnosed with it officially in 04. It is very annoying, with shortness of breath, pounding heart,and feeling like you are running a race which sitting still. I have also had an increase in feeling like it skips a beat. All this prompted the Toprol usage. It does help the heart rate and palps, but now I feel so tired I can hardly put one foot in front of the other. I try to walk for thirty min. at least five days a week, and today it was all I could do to make it. I have to watch my twenty month old daily, and I can't keep up with his energy now for sure. I plant to go back to the 25mg twice a day starting tomorrow, and maybe eventually get to the 25mg once daily. I never would recommend anyone stopped something like this cold turkey, you could find yourself in the ER, never play with any heart meds!! I pray that a slow decrease will be the answer to finding some symptom relief of my condition, yet still being able to function daily. Thank God also I am a stay at home mom for now, starting this and trying to work, I would be sleeping on the job!