cats suddenly stopped getting along

Question
My two cats are 4 years old now, they're from the same litter and we've had them since they were 2 months old. When they were younger they would do everything together -- play, sleep, eat, etc. They sleep in the laundry room at night, have separate beds both in the laundry room and near the fireplace, but share a litter box and food bowl.

Lately the more "dominant" cat has been lashing out at the other cat. I'm concerned because it's been going on for a few months now, and lately it seems like it's worse. The dominating cat can't walk by the other cat without meowing at him and striking him with his paw. The other cat is so sweet to him though, and is always worried if he's not around. He will always lick and sniff the more dominating cat, but this makes the dominating cat swat at him and hiss at him. At first I thought that the dominating cat was just getting annoyed with the other cat and it would eventually  pass, but now I'm worried that this is permanent. The dominant cat can't seem to stand being around the other cat, and we have no idea why. They are both neutered, we haven't moved, there are no other pets, so I'm not sure where this aggression is coming from.

My family was thinking about splitting the cats up for some time so that they have some space, but I was worried that the "weaker" cat would become too upset by this. Do you have any ideas of what we can do to help them get along again? They've always shared a litter box and food bowls, and that doesn't seem to be a problem, but perhaps we need to separate them more? Any suggestions would be extremely helpful.

Also I've read on this site that you recommend Feliway Comfort Zone, but I am a bit uncomfortable with providing some pheremonal stimulant to my cats. If you think that would be useful in this situation, could you please explain why and what it does exactly?

Thanks so much.

Answer
Hi Saira,

It seems there is something else going on. If they were getting along before something has changed to upset the dom. cat. Check around and see if the dom. cat is able to see outside. There may be another cat around that he sees or smell. This would explain the problem. You then need to remove the outside stimuli and things should go back to normal. Did the other cat go to the vet lately? He may have picked up strange smells from there and the dom. one is reacting to those smells. How about new people in the house? This could also set him off. You may want to try to reintroduce them together following a cat intro protocol. Here is a great link that explains alot for you.
http://www.kingstownecatclinic.com/Redirected%20Aggression.htm

Feliway is a very safe product and can work wonders in this type of situation. I would definately give it a try. Good luck. Write back and let me know what happened.

Ciao, Karen