Hi Arlene… Sonny's been experiencing unexplained bouts of aggression for the last 2 months. When I took him to the vet this week I found out his a cholesterol level of 306 and he had gained 2 pounds in 8 weeks (while being on a diet). He is going back on the 15th to have a full thyroid pannel run. My vet however did not feel his sudden behavior change would be due to a thyroid problem. From everything I've read since then I feel that is could definately be a symptom of his thyroid. He's normally a sweet loveable boy.