Did this just happen to your cat recently? Does it seem his fur is dull or oily looking as well?
Does he go outside?
Typical symptoms for hyperthyroidism is weight loss and hyperactivity, but sometimes it's more subtle. There could be changes in fur condition (often matted or oily), increased thirst, becoming aggressive or seemingly frightened of everything. You might also feel a lump at the lower throat area of your cat's neck.
Some cats, rather than becoming hyperactive lose their energy or teeter between being overly active and then lethargic.
Hypothyroidism is a lesser seen thyroid disease in cats, where the gland is underactive. With this type of thyroid disorder the animal is often overweight, sluggish, lethargic and may eat constantly.
Again, fur changes are often seen.
In both cases - treatments are available and must be determined by your vet after a hands on exam. Blood tests should include T3 and T4 blood chemistries.
Other conditions may mimic thyroid disease, including diabetes, so you really shouldn't put off a vet visit in order to insure your companions health and survival.
There is more about thyroid disease here: http://www.sniksnak.com/cathealth/hyperthyroidism.html
And some interesting info about nutritional guidelines that may help support a healthy thyroid here http://www.catinfo.org/
Meanwhile, you may have to just cut the mats out or have a professional cut done (a lion's cut is popular). Many long hair cat owners keep a seam ripper to work through mats like this.
Since the condition recurred shortly after his bathing, having him evaluated for thyroid disease is a prudent step.
Let me know how you make out ok?
Own Animal Care org.
Animal Rescue&Care Org Owner; Animal Care author; Animal Behavior Consults.;Cert. Avian Specialist;
You really should look into the "lion's cut" - I find it unusually attractive
Diabetes could also be behind the changes, or even both thyroid and diabetes.
The vet at www.catinfo.org addresses a nutritional approach that I've found works beautifully. I've got a nearly 20 year old permanent resident who continually checks out with his thyroid and diabetes chemistries - purrfect!
Let me know how it goes. You can re open this question anytime to follow up and you do not have to press accept again.