2 cats suddenly not getting along

have a total of 4 cats, ranging from 3 years old to 4 years old. They have gotten along fine, up until a few days ago. Two of them (SF and NM) aged 7 years and 4 years respectively have suddenly started some nasty and loud fights. Of all 4, they were the two that used to barrel around the house together (I called it race track kitty), they slept on the bed with me, etc. A few days ago they had a fight, deep meows, some screeches etc and then everytime they SAW eachother after that, they would let out the deep meow. They had another "spat" at 5:00 this morning, same reactions. They are walking around "on egg shells" right now. I do have feliway diffusers in my house and have had those for quite a few years, nothing has changed (I haven't moved, I haven't bought new furniture, re-arranged the house, no one new moved in or out, my schedule hasn't changed...NOTHING HAS CHANGED!!). I just can't figure out what happened to cause such tension and aggression between these two....I don't even know what to do when they are looking at eachother growling those deep sounding noises...HELP!!!!!!! How do I get them back to a "happy" place!! It is very upsetting to see them both so upset!!

Hmm, have they been to the vet to see if one of them has something medical happening that might make him or her suddenly change behavior? I know when humans are in pain, they can be hard to get along with ...

Welcome to Pet Talk! Karen may be onto something here. Cats can smell it when another cat is ill or becoming ill and, even if they've been good buddies all along, the stronger cat may bully the weaker, sick cat. My meezer Coco Puff and my calico Puddy were pretty good friends until she started to go downhill w/chronic renal failure and her breath smelled funny. Then Coco Puff picked on her after that. It's a good idea to get your kitties to your vet and see what s/he has to say. A checkup for both of them may answer your question. Good luck and I do hope that things calm down for you. I'm looking forward to a good report. :)

Thanks for the ideas. I actually work at a veterinary emergency facility (have for over 8 years)....Neither is sick, neither have been to the vet recently...I thought of that too, but as much as I rack my brain, there is absolutely nothing that has changed in their life, environment, surroundings, etc...I just can't figure it out! I have some feliway spray, I may try spraying it on a towel and rubbing both cats as well in an attempt to calm whatever is going on between these two. Any other thoughts and/or suggestions would be greatly appreciated, I just want to get them back to where they were before this happened.

Keep a spray bottle handy with water, and squirt them when they start. At least you can let them know this is NOT acceptable. You can't force them to be best buddies again, but you CAN insist they live in harmony.

Good luck with this!