Mom keeps asking to go downstairs to sleep, every night. How can I convince her there is no downstairs?

To answer the question about having sibilings!! Yes, I do and they all are older but not wiser! They all have their own agenda and they all have excuses when it comes to help out. Thank you all for suggestions...

As stated above have your dad tell her that in the morning she can go downstairs it is too late at night..maybe this will help..do you have any siblings that can rotate staying there at night? Just a suggestion...good luck and take care

Advise your dad to tell your mom, the next time she wakes him up wanting to go downstairs, that he will take her downstairs in the morning, that he is trying to sleep. See if that pacifies her for the time being and allows him to get some sleep.

This is so hard for you. Its really hard when someone fixates on something like your mother is. Trying to persuade someone with dementia usually won't work.
My mother in law fixates on "taking her home", when she is alreay in her home.
She fixates on seeing her parents. It takes much patience on our part. Your poor father. Sometimes you just have to tell her something like you will later.... But she will keep fixating and you have to deal with it another time, over and over. One thing we did notice, after we had to put my mother in law back on celexa for agitation and behavioural issues, she has done less of the fixiation. We hope this lasts for her,