At a Loss

My 92 year old father-in-law is currently in a very nice rehab facility after a 5 day hospital stay for pneumonia. He is doing well physically, but had a dramatic change in his cognitive function starting the day after he entered the hospital. He goes from being fairly rational to being very irrational, paranoid, trying to leave the facility, accusing us of trying to take all his money, etc. In the mornings, he is more normal...to the point it's hard unless you really know him to even know anything is wrong. We've heard it called sundowners, but regardless of what it's called, the rehab facility says they are not equipped to deal with this, and after one night of it threatened to discharge him immediately. We had his doc call in some ativan (which they had to use at least one night in the hospital), have a sitter staying with him tonight so we can hopefully get a little sleep without being called at all hours to come and calm him down, and are moving him to a memory care facility tomorrow and praying that he can settle there. If the memory care facility (locked unit) winds up not being able to handle him, what other options are there? He cannot go home due to the confusion and fall risk, and we are at a loss if this doesn't work out. Would appreciate any ideas.