How do I deal with my Dad (81) who has Alzheimer's and at bed-time he gets agitated, responding to voices, then becoming aggressive?

I learned about some of the ways to de-escalate my Dad during the day, most of them work. But at night sometimes the behavior escalates, refusing to go to his room at bed-time, yelling at voices, repeating different words, asking himself questions, then answering them. Then when he finally goes to bed, he continues the behavior. How do I go about getting him to calm down? When I try to re-direct him, he just says,"I'm alright, yes sir, I'm alright." Then go right back into the behavior in a lower tone, revving up louder, and louder, getting angry, into fierce voices. I called the Doctor,(he ordered another sleep med) it worked for the first 2 nights, he slept pretty much all night. But now he's back to the yelling, the behavior, & the voices. How do I help him?