Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am very sorry to hear that your fellow drooling excessively and refusing to eat or drink for the past 36 hours.
Drooling can be a sign of nausea but it can also be a sign of oral pain due to an infected tooth or a foreign body caught between his teeth, on the roof of his mouth or in the back of his throat. Sometimes it is a sign of an oral tumor. Since he is a younger fellow nausea due to organ failure is possible, but less likely.
It can also be due to a nerve problem that is making it difficult for him to control his tongue or close his mouth properly.
I do recommend rinsing out his mouth with cool water several times.
I know that may have you looked in his mouth but sometimes it takes a very close look under sedation to find the problem. If he will let you examine the inside his mouth again closely for swelling, reddened areas or any sign or trauma or a foreign body.
Since this has already persisted for 36 hours it is time now for a veterinary visit. Because he isn't eating or drinking I am very concerned about him. He will quickly become dehydrated and as his liver breaks down fats for energy to live he may develop a type of liver disease called hepatic lipidosis, which can be difficult to reverse and in some instances can be deadly.
In the meantime in case this is related to nausea you can give him acid reducers to try and settle his stomach. Either:
1) Pepcid-ac (famotidine) at a dose of one quarter of a 10mg tablet per 5 to 10 pounds of body weight every 12 hours.
2) Prilosec (omeprazole) at a dose of one quarter of a 10mg tablet per 5 to 10 pounds of body weight every 24 hours.
These will reduce stomach acid and should help settle his stomach. These are quite safe and can be used for several days if necessary.
A couple hours after one of the acid reducers is given try offering small amounts of water or broth to drink. If he still won't drink he must see a veterinarian.
If that goes well then late today or tomorrow start a bland diet of 2/3 boiled, lean, white, skinless chicken and 1/3 plain, boiled, white rice. Give small meals several times a day. Feed the bland diet for several days, then start mixing in his regular diet and slowly convert him back over a period of 5 to 7 days.
If his drooling and refusal to eat and drink continues in spite of using an acid reducer and a bland diet then he should see his veterinarian for an examination, some blood tests to look for underlying metabolic disease, probably sedation to look closely in his mouth and take dental radiographs.
Please let me know if you have any further questions.