Mitral valve surgery gone awry?

I recently had open heart surgery for mitral valve regurgitation (moderate to severe).
Prior to the surgery I was very active. I had low blood pressure, EF levels ~55-60% and rode my bike hundreds of miles per week, went on multi week, self supported, bike trips (eg. Artic Circle in Norway) and, at 79 years of age felt great. I had previously had an ablation to control AFib and was in normal sinus rhythm at the time of the surgery.
After my mitral valve replacement, all hell broke loose.
I gained 20 lbs of fluid, was put on a high dose (15mg/day) of midodrine because my blood pressure was so low (~80/50) and my heart rate was consistently over 100 bpm.
My diagnosis was now systolic heart failure (EF 30-35%).
After 14 days post surgery in the hospital I was released since my body rate returned to previous levels (~145 lbs).
I have been recently prescribed Metropolol to lower the pulse (which was questioned by my visiting nurse and pharmacist).
I feel like crap.
I am beyond wonderment as to how I entered the surgery as a “young-ish” feeling man and came out as an old man!