N.J.
My girls used to do it a lot, but over the last 1 or 2 have not be so <lack of a better term> worried about it. I delt with it like this.
One of them would be sick, and throw up. When she was over being sick, she would still run up to me and say mommy I have to frow up. <sorry, she used to say it so cute> I tell her to run to the bathroom. I would ignore her and not make a big deal out of her being sick. Even if I was worried, I didn't let it show to her, and basically come across as it not being a big deal. It could be a way for her to get your attention. My girls still sometime obsesse about something that happened to them. They usually have to tell someone about it, and I ask them if they are sick right now?, ans they say no, and I say don't worry about it then. Your not sick now, so please stop talking about it. I also would tell them that they are fine. I guess I sound kinda mean, but if you give her a ton of attention over it, she's going to keep doing it. If she genuanly <sp> sick, then attention is called for, but if she fine. Tell her she is, and to stop worring about it. I would also tell the girls that if they were really that sick, we would have to go to the doctor and they might have to get a shot since they were sooooooo sick. Then ask if they want to go to the doctor. There answer would be no. If by chance one said yes, then I knew they REALLY didn't feel good. Gosh...I sound really mean. This is what worked for me.