cat will not eat, losing too much weight

Hoping someone here might suggest helpful remedies for this situation. Our family cat is 13 years old, in good health. No particular health issues other than a tendency to overindulge and then regurgitate food when her stomach becomes too full. She tends to also be less active and more sedentary than some house cats. She gets a bit anxious if the rest of us are outside, and will sit by the window or door, meowing. When she was a kitten, she would get a puffy lower lip/chin from eating a certain type of cat food, so we switched to something else. This does not happen as an adult cat.

Because of her sedentary ways and her tendency to overfill herself, she was too heavy and it was recommended we try a food puzzle, which is something (in this case, a ball with adjustable holes) a cat plays with in order to get the treats or food to fall out a bit at a time. This prevents cats from eating too quickly / too much at one time, which can lead to regurgitation and the habit can lead to weight issues, which then causes other strain.

We tried the food puzzle and she seemed to enjoy batting it around to get her food; advocates (including vets) say that it mimics what a cat does, to hunt down and pursue food, and to eat very small amounts (whatever they find or catch) several times a day, instead of feasting at a bowlful of a days worth of food.

The cat lost weight and continued to use the ball and look forward to our filling it in the morning. However, at some point, she started throwing up just water. Cats need to drink a lot and I got the sense that she was drinking too much water at once and without as much food in her stomach, the water came sailing back up. As she had lost sufficient weight to a healthier size, we stopped the food puzzle, leaving some food in the puzzle while also resuming her dish of food, so she could choose from them both.

Instead, she has stopped eating. I tried switching to a wet food and it was initially met with enthusiasm, though she mostly seems to lick the gravy out of it. I melted gelatin in hot water or broth or use a bit of broth and spooned it over dry kibble to entice her, and initially she showed interest but no attempt lasts more than a day and overall she is not eating sufficient amounts of food to prevent further weight loss.

Her former stool habits before the food puzzle was a daily or every other day stool, soft and formed. Once she used the food puzzle, her stool became less frequent, smaller and with less odor. Now days pass without any stool in her litter box. When one comes out it is an inch long or so, and very hard. Her thirst remains unchanged and she does plenty of urination in her litter box. Her eyes look watery and tired. She displays no respiratory symptoms like a cold virus, etc.

We do not know whether she has constipation or something, which discouraged further eating until it passes, or whether she has mouth / teeth discomfort of some kind (no history of this), or whether she has some other internal issue due to age. Or whether it is the stress of the change of routine to the food puzzle, though she seemed to like it at the time. She is now too thin, and due to lack of food intake daily, seems lethargic and disinterested. At times when she overindulged and had digestive issues, I gave Nux vomica 30c (a commonly recommended remedy for pets) and it always righted what was wrong. She does not seem to respond to it in any obvious way this time.

Any suggestions based on this description would be much appreciated; were desperate to help her get her appetite and energy back.
[Edited by missingmyth44 on 2024-06-27 02:02:53]