You're speaking with Dr. Michael Salkin. Welcome to JustAnswer. I'm currently typing up my reply.
Amber and Simon, if this behavior has persisted from a year of age and now abated when confined to a room and there's been no change in weight, I see no reason to consider a medical disorder. If he were an older cat, hyperthyroidism would be a consideration but hyperthyroid cats don't improve without therapy and it would be unusual to diagnose hyperthyroidism at even 5 years of age in any event. I have no objection to having a basic diagnostic panel of blood and urine tests performed but I would be surprised if you found anything untoward in such tests.
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Idiopathic cystitis - a non-infectious inflammation of the bladder thought to be stress-related. A complete urinalysis usually reveals increased numbers of both red and white blood cells but no bacteria. His normalizing when relocated rules out metabolic disorders.