My Father had CHF when he was 42, resulting from a massive MI on the LAD. His EF was down to 14%. He had gone from perfectly healthy to end-stage CHF overnight. His biggest issue was O2 sat, as fluid was filling his lungs and he couldn't absorb O2. This stained his entire body. He was put on lasix and waited at home for the transplant. We speculate that he handled this well because he was very healthy before it happened, he hadn't lived this condition very long.
He was placed on a heart transplant list. After 5 months he received his heart transplant. The lasix helped short term and he was fine from what I could tell. This was back in 1988. He's lived a very full life post transplant. It's hard to believe that his 25th anniversary is coming up. He's still going very strong and while he could retire from work he hasn't. If you ever met him you would have no idea.
As for your new symptoms, it could be viral (you are sick) or something else... Any time you have a change in symptoms you should call up your physician and let them know.
Have you strategized with your cardiologist about where this is heading and what the action plan is?
My best wishes, sorry I can't give any good news but ask if your EF has been stable? A bad sign is deterioration... I don't know about the back pain or weight loss, but too may not be definitive.
Tiredness would follow, from the low EF, so too: is that stable or changing?
I don't think anyone on the Community would venture a guess on life-expectancy, but answers to the questions above may help uncover some hope.
Did your doctor give you a number?
I have an enlarged heart, in the atria area due to valve problems. In 2007 recommended I see a surgeon about getting the mitral valve replaced or repaired if possible. When I asked what if I don't, he said 5 years. I got the surgery done, and here I am just over 5 years later with the valve repaired and the heart enlargement about he same, stable.
I am not saying this has any direct application to your question, just a data point and example of a cardiologist who was ready to give me a "number". My EF has always tested in the 60% or better range, so that was not a factor in my decision... nonetheless I suffer from fatigue/tiredness and some dizziness from my medications and the reduced efficiency of my heart due to permanent atrial fibrillation - this we have not been able to fix/stop.