Hi Doctors, My Husband Is 36 Years Old, For Almost

Hi doctors, my husband is 36 years old, for almost 2 months now we have been back and forth to the Dr office trying to find out his problem with no results. My husband is very active and healthy. He works out at least 5 days a week and he feels some better after he works out. Then in just a few hours he's feeling bad again. His symptoms are, very fatigued, he runs out of energy real quick, finds it hard to breathe at times, no energy to move or get up, he stays off balance (not dizzy), he stays thirsty for water he says he feels like a dry mouth. He has been to the eye dr where they told him there's nothing wrong with his eyes and he has perfect vision, had a brain MRI which showed nothing abnormal, he had an EKG which came back normal, he's bloodwork (a normal bloodwork up) came back normal, a CAT scan which came back normal, a chest x-ray which came back normal, no vertigo, nothing viral. So he's on the couch as I'm typing this, asleep. I've been trying to get him to go to the ER but he says why they won't do anything and can't find anything so I'm wasting my time, I don't feel like going and sitting there because I'm exhausted. He is just so tired and pale. I'm really at a loss to try to see what's going on. I was hoping you may have some insight on something else we could be tested for? We just really need answers, he's not really been able to work, he goes in and normally back home withing fours hours if not sooner. His first symptoms were being off balance and all the other symptoms have gradually come on. I was thinking him fighting being off balance all day may be causing the other symptoms to be worse. I've known my husband a very long time and this is not his behavior. I'm very concerned that if this is something serious and it doesn't get caught in time we may have more serious issues to deal with. Thank you for time
Concerned wife