Cat all of a sudden not getting along with the other cats
My older cat came down with a severe upper respiratory infection that lasted over a month. While he was sick he was isolated from the other cats. He now feels better, so I put him with the other cats. He immediately ran under the couch and started growling and hissing at nothing. I figured he would calm down and get used to being around everyone again, but it's been three days and he's still doing it. He did move out from under the couch and into a corner behind a shelf, but he just sits there and hisses. he's not eating and when I picked him up today, he peed as I was picking him up. He's scared to death of being in the place he's lived for the past four years. Last year he was quarantined because of an illness and he did not do this. He is a very friendly cat who purrs at the slightest touch and even give hugs. He has has never minded the other cats, even when he first came to live with us. In the bathroom,(his quarantine area), he was as friendly as he'd always been. Currently, he is sitting on my lap. He's staying put, but if I pet him, he growls and hisses lightly. It's all very strange.
We know that cats dance to their own drummer and that its independent streak can wreak havoc with what we think is normal and what we consider unusual. However, sudden feline behavior changes can be a signal that “all is not well”. You didn’t mention how old your cat is, but an aging cat can have behavioral changes. If your cat isn’t aging then there is another underlying reason for this moody behavior.
The main causes for this behavior change in your situation could be that a health problem remains (not necessarily the same one that he was quarantined for) or the change in the location from a private room (bathroom) to being back in the feline communal areas doesn’t sit right with him and is making him stressed. He could also be fearful of the other cats after a month long isolation without anything to worry about. When a cat feels threatened (real or imagined) he may change his behavior to be more aggressive even towards people he cares about (like you). He displays this “fear aggression” with hissing, spitting, growling, etc. The peeing when you picked him up also sounds like its fear related…but it could be a medical issue.
Pain or health problems can cause the hiding behavior that you mentioned. Depression can also be a factor. Perhaps the isolation was longer than the last time when your cat didn’t display odd behavior when re-introduced to the cat populace. Another possibility is the change is temporary and he’s being defensive and guarding what he considers his own personal space.
You have said that his behavior has been going on for 3 days (as of yesterday when you wrote the note). What concerns me the most is that you said he isn’t eating. This can bring on fatty liver syndrome which can be very dangerous. Behavior changes that last for this length of time should be a cause for worry. The cat should be taken to the vet and examined for physical problems. If there is no physical reason then it may be a diagnosis of anxiety. Identifying the cause of the stress will be important in order to find the most suitable treatment. The vet may prescribe medications or alternative remedies.
I’m hoping that this situation has resolved itself since another day has passed but if the problem still exists, take your cat to your vet so at least you know if it’s physical or stress related. I hope you have him purring and hugging again soon.