Hello, sorry to hear about your husband, I can understand how this change could be worrisome, hopefully I can shed a little bit of light on the situation.
First of all I'll ask about his sleep habits... How much does he weigh? Does he snore, or have long pauses in his breathing while he's sleeping? Has he ever been told he has sleep apnea?
How much weight has he lost, and over how long? Any fevers/ chills, night sweats, or other changes you've noticed?
Any other chronic health problems?
I'll wait to see what you can add, and then go from there, thanks...
Well, my first thought would be that he has Obstructive Sleep Apnea. This can cause all of the above symptoms that you speak of, especially the daytime sleepiness. Here is a link which has a lot of good information about the condition, it's causes and treatments.
http://en.wikipedia.org/wiki/Sleep_apnea
It is very common and can be dangerous most especially because people often fall asleep doing tasks, such as driving. There are also the associated health complications which are mentioned in the article. There are a couple different treatments for this, most commonly a machine that hooks to a mask that goes on your face while you sleep. It pushes air in to help you oxygenate, and get the quality sleep necessary. Most people have a difficult time getting used to the machine, however, I will stress that if they get through the initial phase, they will be very pleased in the quick change in increased energy, wakefulness, and getting rid of that "old man" look you speak of.
So in closing I would go to your family physician, and they will most likely recommend a sleep study at a facility where they monitor your husbands sleep, and can make an official diagnosis. I hope this helps, I wish you the best of luck...
Doctor
Bachelor in Nursing, 3+ years nursing experience, Doctor of Osteopathic Medicine