Please have him checked for sleep apnea. If they say he doesn't have it, find someone else and have him checked again. By the time my husband was finally diagnosed, after six years of the symptoms progressing, the test results came back that he was stopping breathing more than 70 times per hour. The longer it goes on, the greater the impact on his heart and brain, due to lack of oxygen. It got so bad that I wouldn't let him drive with the kids in the car because he couldn't stay awake at work, and would nod off while driving. I didn't want him driving himself even. Due to his lack of focus and the constant exhaustion and inability to stay awake, we had almost no relationship left by the time he got his CPAP maching, but within days, he was almost back to the man I fell in love with. Don't delay, get a second opinion.
In the meantime, get him a back wedge, which might help because gravity helps keep their throat open. There is also a throat spray that numbs the throat muscles and helps prevent them from collapsing, in milder cases. Good luck.