@retirement75
Many things can cause a low EF and heart failure. Many women when pregnant come down with heart failure and recovery months after delivery. Medications can affect the heart negatively just like the do positive affect.

One of cardiologist described heart failure this way. "On third will get worse, one third will stay the same, and one third will get better." Symptoms can change. My EF has been the same for over 10 years. I am at 22%.

A normal EF is 50-70. So if your EF is 50 it is on the low end but still normal. Many many drugs can cause fatigue. When I started Entresto and Carvedilol I had extremely high fatigue. I thought would not be able to take. My doctors (all at Mayo Jacksonville) told me takes time for body to adjust to those drugs and hang in there as will get better. I did, and it did.

I had a allergic reaction to Spironolactone and had to switch. Your doctors suggestion that sleep apnea may be causing your fatigue is correct. It can also affect heart failure. I am getting ready to do another sleep study to see if sleep apnea is present. It was ordered by my electrophysiologist as can contribute to heart failure, PVCs, PACs and VTAC.

Talk to your doctors about you fatigue and see if you can do exercises that will help you with your fatigue. I know sounds like "what" but your body needs exercise or muscles atrophy and you will have fatigue.

I know when I went through prostate cancer radiation treatments I was told that a common side affect was fatigue and my R/Os told me to try to keep walking as will help with the fatigue. They were right it did come on about half way through but I was already walking to keep it from being severe.

I recently had weakness in my thigh muscles and my heart failure and primary care doctors asked me to do specific exercises to strengthen those muscles. You did not mention your age (I am 79) but my doctors say with age muscles will lose muscle tone and need to do strengthening exercises. But like exercising you need to get your physicians to approve and recommend what is best for you.