Vomiting, inappetace and weight loss can be caused by a number of serious things but I am particularly concerned about the disorientation. Causes can include gastrointestinal blockages, systemic disease like liver or kidney disease or toxicity. If he has not been eating for a number of days, plus vomiting he is most likely dehydrated and malnourished. I expect he will need a drip to stabilise him. The first thing your vet will do is a full physical examination and run some blood work to get an idea of what his condition is. Further testing and treatment will depend on the results.
Your dog is extremely ill, I urge you to seek immediate veterinary attention.
Your dog is extremely ill, I urge you to seek immediate veterinary attention.