Stress, I would guess, could be a cause of hair loss-hey, it is for us!! It's a very good idea about keeping him in for a few days. He might drive ya nuts, though, but it would be worth it!! LOL. Thyroid issues could show up as constipation or diarrhea. And, you didn't mention whether there's been any weight changes. For peace of mind, I'd take him to the vet and ask for a thyroid test, and he's probably got more ideas as to some other possible causes!
Let me know how everything goes!
He's eating and drinking fine, the only thing is the hair loss, he's not out of sorts, usual cuddly self. Don't know about potty as he goes out for that. Might keep him in for a couple of nights and see. He did shed about four years ago after being in a cattery for 3 months and took about a year for it to settle, we put that down to being in the cattery, although they were lovely and he got lots of cuddles, then moving into a new home. We got a puppy a few months ago, but they're not really interested in each other and tend to ignore each other. He's also in charge, allowed on the sofa and beds and the dog isn't, but wonder if he's a bit stressed.
You are right, I'd also expect the cat's coat to get thicker NOT thinner! I'd go to the vet and ask for tests to see if he's got thyroid issues. How's the appetite, potty habbits, and his thirst? And has he lost weight lately? I'd also get him checked for diabetes, and kidney problems which are also common in cats that are 7 yrs and older!
Let us know what the vet says!