Get Your Dog Care Questions Answered by Experts
Vestibular disease, tumors of the cerebellum and inner ear infection, are the major possible diagnoses for the signs you describe (blindness, lack of coordination, falling, not eating/drinking, confusion). Look at his eyes and note if they are moving rapidly from side to side (nystagmus). If so, the most likely diagnosis is vestibular disease.
If you have 81 mg baby/heartsmart aspirin, you could give one. It may not help particularly since he is already on Prevacox, a non steroidal antiinflammatory. However, it will not hurt. Do not continue the aspirin after the one dose because the side effects of non steroidal drugs,particularly the risk of gastric ulcers are additive.
Keep him warm, quiet and secure whether that means having him near you or in the crate. Often darkness keeps them quieter than light even if they act blind. Offer him water. He most likely will not eat. Carry him out to urinate, if possible and support him. If you can not carry him and he is lying down, put something that will absorb urine under him and change when wet. If vestibular disease is the problem, his condition will improve with only supportive care over several days and can return to his normal within a couple weeks.
Does your mobile vet do emergency hours or return emergency calls? I ask because I do and am a mobile vet. If so, perhaps you can get your boy seen tomorrow. Otherwise, schedule an appointment for early Monday. If he goes downhill, you may need to think about the car, but your description sounds like that is best avoided.
Let me know if you have follow up questions.