It looks like your uncle had some pneumonia
which got very severe and hence now has went into a metabolic encephalopathy
(a stage like coma
Why this happen is very difficult to explain without seeing any xrays and reports here but what i feel from the description that he must have had some acute viral infections like influenza
His age is 80 and hence the infections do cause a faster deterioration in people of his age.
WE WILL PRAY FOR HIM TO GET BETTER SOON