I have a 2.5 year old cat that I adopted last year from a local animal shelter. In this last one year, he became real friendly and talkative. About two weeks back, he suddenly started acting strange. He has become fearful of everything, including me, my wife and my daughter. I took him to the vet thinking he was probably sick. Vet did a complete checkup and said that cat was fine. The problem is my cat doesn't even want to go to his room. It seems he has forgotten everything. I have been putting food bowl near his mouth so he could eat. He has forgotten how to climb up and down the stairs or chair near window. This morning he sought my help in putting him down from his chair by meowing. He used to run like a puppy chasing ping pong balls. Everything has stopped. I thought it was a temporary phase but now I don't know what to do. Has anyone experienced this kinda behavior? Any help or advise would be really appreciated.