He was like a zombie, couldn't remember dates or times, just people. Would sleep all day, rock back and forth, get up and down, over and over, now he isn't doing that anymore, what's up?
Perhaps the pain from his bad hip made him worse and he no longer has the pain? Perhaps the anesthesia had an affect? My understanding is that dementia fluctuates. Some days are better than others. Have you spoken to his neurologist about the improvement? Regardless, enjoy this time.