I don't know if you can compare dogs and cats symptoms, but we noticed our cat's voice had suddenly changed. She was losing her meow. We mentioned it to our vet when we took her in for her yearly vaccinations a couple days later and they did a blood test. Luckily, we had a recent blood test from about 3 months earlier when her teeth were cleaned. (They did that test because she's elderly.) Anyhow, by comparing the results, they were able to diagnose her as hyper-thyroid. We caught it early before any damage was done and she now is doing well on medication. Might not hurt to check.