At 3:00 in the morning Mark woke up because she was yowling (the kind of noise they make when they go into heat). She has done this a couple of times before, and if we don't let her out, then she starts to pee in the house. (I knew she was acting very strange last night) We have talked to the vet about it, and they think that when she got fixed, they missed some ovarian tissue, so her hormones get messed up and she thinks she is in heat. I worry about her when she gets like this, but thankfully it will only last a day or two.