My cat Sissy has had a rough month so I suppose that could be the cause but I'd like some other opinions. She was the most laid back and mellow cat but over the past month she was in heat for seven days, then she got sick (vomiting due to constipation and possible enteritis according to the vet). Once she got back from the vet she started eating and drinking without vomiting the next day and the day after she had a bowl movement. After she came out of heat she started lashing out at her sister and once she got sick I figured that was why. Earlier this week she seemed to be in a better mood but the other morning she lashed out at my husband as he was petting her and she just lashed out at me for petting her (she was near her sister at the time). I was shocked and frankly heart broken when she lashed out at me because she has never ever been even slightly angry with me. Her sister is currently in heat so I don't know if that could be irritating Sissy or not. We have been keeping her sister in a spare bedroom with food, water and a litter box and also letting her out frequently.