Unfortunately we don't know. We have some ideas, but nothing for sure. My old vet (we moved this past spring/summer) had every test she could think of run on our kitty and even set us to an e-vet/specialist to run a couple of other tests. This has happened over about 8 years. This time we were visiting the town we used to live right when it happened so I just called and they had the meds ready for us when we got there to pick up. I do have a really good new vet, but she hasn't seen Tiger yet. At this point the only two guesses we really have are that she does not digest vitamin B properly or that she gets a hairball throws up thinks that she got sick because of eating, doesn't eat and doesn't get sick. Those are the only two things we can come up with. She actually made it through all the stress of selling our house, sending all three of our kitties to my parents home (in Ohio) while selling house and moving and bringing them here. We got moved here in June and got them in July. She stopped eating again at the very end of Oct. Now she is better at this point than there. At that point she was not eating at all. Now she is eating some wet food and some dry food, but not enough yet. Even though I'm getting frustrated I must also remember she does get her strength back before she gains weight and she is not hiding, which she does when she is not eating at all. She is also 13 years old at this point. Although age is not the issue since it's been happening since she was around 5.