Hissing Cat

Question
Hello, Norman
I adopted two cats about a year ago.  They were both from the same litter and loved each others company.  A few months ago my female cat died, and for a short while her brother--the one I still have--seemed to be very depressed.  A short while later I got a new cat to keep him company, I knew that I would have to gradually introduce them to each other.  It took about a month and a half for them to start getting along, and since, they have be the best of buddies.  I have noticed--in the past week--that my older male cat has been hissing at me any time I open the door--weather I am coming or going.  Any time I get near him, to pet him or give him a treat, he will do the same thing.  A few times I have tried picking him up and giving him attention--he used to purr nonstop when I would do this--but now he curls up into a tight ball and looks as though he is afraid his life is going to end, or that he is going to hurt me in some way.  He is not fixed at this point, could this be in connection with his mean behavior?  Or is there some other reason he could be acting this way?
Thank you,
Brandon

Answer
Brandon,

Getting him fixed would be a good thing to do.  However, if he has had a sudden change in behavior, he may be in pain, so a visit to the vet for a full check up may be in order.

Please let me know what you find.

Best regards... Norm.