Hello and thanks for trusting me to help you and your pet today. I'm a veterinarian with over 25 years experience and would be happy to work with you.
There are very many reasons why cats vomit, some more serious than others. Vomiting is a vague sign that can be associated with simple things like dietary indiscretion to more serious things like intestinal obstruction or metabolic disorders. In young cats, we usually are a little more worried about foreign body ingestion. We decide how aggressive we need to be in diagnosing and treating it based on how severe the symptoms and how long it has been going on.
In your cat's case, since this has been going on and he is now lethargic, I would be very concerned. The foul odor can be due to various things,but two of the most common would be either kidney
disease or diabetes
, both which could also lead to the vomiting and lethargy.
I would not advise that you wait until tomorrow. It would be best to seek emergency services if at all possible. By tomorrow, he could end up being much sicker due to the metabolic abnormalities that can occur during many diseases.
I hope this is helpful. Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please reply so I can clarify for you.