Hi, My 96 Year Old, Sharp As A Tac, Very

Question: Hi, My 96 year old, sharp as a tac, very lucid, logical mom has been getting up at night pacing and seems nervous. then goes back to bed and a few hours later does it again. The past two nights she has been panicky and delluisonal. She is at my house for 2 nights. She is paranoid I wont let her go home and afraid I want to kill her and that she will never see her house again. the second day I brought her home and she was happy to be there and logically explained how safe she feels in her own house and everything is familiar. That evening my sister stayed with her. my mom called me at 4am apologizing that she was wrong, it wasnt me that she thought wanted to kill her it was my sister. I went there at 5am I was scared for her. over the next few hours she became very lucid and agreed that was crazy thinking and she doesn't know whats going on. I am so scared for her and confused when all day she is great and sharp as a tac. She is up on all that is going on in the world, reads papers, wacthes news, calls friends, family, we go out shopping...What is going on at night time. I feel she should be in a hospital when this happens, in the daytime she is great. I am so sick and confused by this