This may be bile reflux syndrome where when the stomach is empty, bile from the intestines goes into the stomach instead of going down the intestines. This bile is very irritating to hte stomach and will cause vomiting. There is amedicine your vet can prescribe called metoclopramide that helps this condition. It makes the stomach and the upper part of the intestine contract toward the intestine so the bile can't go back to the stomach. If the cat is doing this at night, then you would give it before you go to bed.
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Dr. Louis Gotthelf
Animal Hospital of Montgomery
Pet Skin and Ear Clinic
