We have a chihuahua cross, she's about a year old. Usually she's really hyper and wags her tail and gets under your feet all the time but today we have noticed that she's not interested in anything,not even food, vomits up a little spit now and then, just not herself, looks lethargic. I really hope it's nothing serious. We have had some problems with our neighbour who throws water over both the dogs when they bark and i was beginning to wonder whether he may have poisoned them by throwing over some contaminated food over the fence? I know this is far fetched but i could'nt rule it out.
Sorry to be blunt, but if it is poison it is unlikely she will survive the night. If she does, then get her to a vet first thing in the morning anyway. However, most poisons would have a fairly quick effect, but if she has been like it all day she could just have a bit of colitis. Could even be a blockage, so the vets needs to check her.