I am sorry your kitty is having trouble. There are several things that may be going on with your kitty. Cats are considered to be geriatric at 8 years old, and are prone to illness as they age. The 3 most common ailments known to afflict elderly cats are diabetes, kidney disease and hyperthyroidism. The symptoms include vomiting, diarrhea, increased water consumption, increased urination, dehydration, weakness, muscle wasting, weight loss, poor hair coat, changes in appetite, changes in behavior and increased vocalizations. Your kitty may be experiencing dangerous fluctuations in his blood glucose levels which is making him disoriented (typically seizures accompany these fluctuations). He may be experiencing very high blood pressure that has caused his retinas to detach and result in blindness (can be typical in cats with hyperthyroidism and kidney disease. This blindness is temporary and reversible if treated early on). Your kitty may have a brain tumor, or tumors in other organs that are causing his disorientation and blindness (this is usually accompanied by seizures as well). Any of the above conditions can cause sufficient dehydration to result in the disorientation you are seeing.
I am pretty worried about the hydration status of your kitty, and I am also concerned about the weight loss you are seeing. It is very dangerous for cats to go without food, and if enough weight is lost, they experience called fatty liver disease. This illness is life threatening and is basically one step away from liver failure. This type of complication is something your kitty cannot afford on top of his existing but as yet undiagnosed illness. I think he should be seen by an emergency vet tonight for an exam, comprehensive blood and thyroid panel and a urinalysis. He may also need some radiographs depending on what the vet finds when an exam is conducted. Cats instinctually hide illness, and are often suffering from advanced stages by the time symptoms become obvious. The longer your kitty goes without medcial attention, more dehydrated and decompensated he will become, and the more expensive and difficult it will be to make him well again. Please let me know if I can be of further assistance. If this has been helpful, please hit the green accept button. Good luck with your handsome man!!!