Sounds like an extreme case of what I face. DH had a heart attack and bypass last year followed by a hospital-acquired infection that nearly killed him. He had lost three of the six stone he needed to lose, ideally, by the time he was discharged from hospital. I thought it would be a real stimulus to lose the other three stone. Instead he has put most of the three stone back on.
I am actually puzzled by how much he has put on, because he is quite active. Within weeks of coming home, he had the builders in to start on our delayed extension and since he was, designer, projecct manager etc etc. Within weeks he was climbing ladders to look at progress, putting up gutters etc even though he has been left with repiratory problems and cannot wear a mask. He does snack, mainly cheese and jelly babies, but not excessively, and he gets portion controlled healthy meals, because I am, and want to stay, a healthy weight.
Your DH's excess sleeping may be caused by 'sleep apnoea'. This caused by fat round the neck blocking the airways to the throat, so that he keeps having microwakes when he has to gasp for air, which means he is actually getting very little sleep a night may be as little as 30 seconds at a time.
DH was diagnosed with this some years before his heart attack and had/has to wear a special mask at night that pumps air into his airway to keep it open. His weight loss cured the problem. His weight gain has brought it back.
However, if you can, get your DH to see a doctor and ask to be tested for sleep apnoea. DH was sleeping all day before he got the mask. After one night with the mask, he woke at 7.00am and didn't sleep all day.
If he has that problem, and he seems to have all the symptoms, then just getting that sorted so that he gets a good nights sleep may make a lot of difference to his attitude to life, exercise, and eating.
I so sympathise with you, there is nothing we can do. DH knows how I feel, but I have given up saying anything.