Cat vomiting clear foamy liquid

My 5 year old cat vomited up her food this morning, and since then has been vomiting clear foamy liquid. She has never done this before. She is up and moving around somewhat, but is currently hiding under a bed. She normally rubs up against me, but isn't doing so today. She's allowing us to touch her but isn't really being her normal self.

I am having a similar problem with my approx. 8 year old female cat. She has been like yours since last Sunday. The vet found nothing wrong with her from blood work, no temperature, just dehydrated. I am probably going to have to take her back to the Vet. She hasn't eaten much, just once, when I tried a new food brand, she ate a lot, but then at bed time vomited it all up, looked undigested. I think she is weak from lack of eating. Just a few licks of broth on the food I try to get her to eat. She hasn't ever been outside since I have had her, almost 2 years with no troubles so not eaten anything bad. She is just very timid and gets bullied a lot from my older much larger cat.

@MinervaTheCat:  This is something only a vet could really help with. There are too many things that vomiting could mean. Occasional vomiting, like one or two times a month or two is nothing to be alarmed about, but a lot of vomiting in one day is different. Especially if the cat is not acting like herself. Mine is always a little stressed and uncomfortable right after vomiting, but she gets over it within about an hour.

Are there things out around the house she might have eaten? Plants? Are all chemicals locked away? Has she kept any food down since the initial throw-up?

@Talos: That's annoying, they couldn't find anything? You need to get some kind of food into your cat quickly, because they can get liver problems from not eating and that is very serious. Have you tried small amounts of wet food or plain turkey/chicken baby food? You can also supplement with a high-calorie gel, just look in the medicine area of Petco/Petsmart.