Best friends, now enemies... please help

Hi everyone. I have two cats, a very large round tabby named Broccolli and a much smaller cat named Gargomel. We've had them both for about 2 years and they've been the best of friends since they met. They clean each other, eat together, sleep together, and play together. However, recently we were woken up at 1am a few days ago to find our bigger cat, Broccolli aggresively hissing and chasing the smaller one around. Our smaller cat, Gargomel was also growling and ran into a corner behind some cabinets and pee'd in the corner. (He's never had a litter box problem). Ever since then, they can't stand the sight of each other and we've had to keep them seperated, one in the living room and one in the bedroom. Their behavior toward us hasn't changed at all, they are both still loving and affectionate toward us but can't stand each other. What could have caused two cats who got along great for 2 years to suddently hate each other? Also, both our cats are neuteured so I'm not sure why Garogmel pee'd in the corner, he might have just been scared. If you have any advice or suggestions, pleasee pleasee help.

When you have more then one cat in your home they will normally workout their dominance hierarchy among themselves. Some times the Aggression can occur over competition for some item or your attention. Male cats will become competitively agressive with other males when interested in a female in heat,, You can avoid competitive agression between cats in alot of ways:
1. Have ur cats neutered(CHECK)
2. Avoid having them together in the same space. Overlapping territory can cause fiercer comeptition for attention.objects, or anything else
3.Let your cats work themselves out on ther own.Stay out of conflicts uless the cats really lay into eachother.
4. Keep the food seperated
5. Give them both individual time they want to feel wanted and loved by you. ignoring one for the other increase chances of conflicts to happen.
5 . Provide with toys so that it can act as a distraction.

Well i dont kno what else to think of

Yes DEFINATELY!

I would suggest you take the cat being attacked to the vet fairly quickly. When cats have been together a long time, and one of them becomes ill, their scent changes, either subtley or drastically, but the scent is different causing the other cat to attack the alien cat because of not being able to figure out it is the same cat. It really is an early sign of illness- and that should be ruled out first before looking at other dominance issues, they have more than likely figured out their heirarchy long ago-