Grandpa's cognitive abilities is worst than ever. Is it delirium? Why does this happen? Does it get better?

The first time he got seriously hospitalized it seemed like he lost touch with reality and when he returned home after a day or two he returned to normal. Since then it happened a few times and he recovered.

Now it seems permanent? It gets a little worse every time I see him. In the past it was episodes, but it seems like it's just declining now. What's your experience with this? Is it medication or mental stress? Or both? I don't know much about delirium to be honest.