Can great strides in therapy reverse themselves dramatically in a Alzheimer's/Dementia w/Lewy Bodies situation?

My husband was diagnosed with Alzheimer's/Dementia with Lewy Bodies 6 months ago. For a period of the next three months, he seemed to be in a "freefall" situation with every day resulting in some new setback, such as hallucinations, Sundowners, confusion, etc., with the end result of him being hospitalized after falling twice in one day. From the hospital, he went into a therapy facility for 3 months and has made dramatic progress. He no longer needs a wheelchair, he is no longer falling, he seems more alert and less confused, more "himself" in other words. My question is this: can this amazing progress suddenly reverse itself given the nature of his diagnosis? I assume he will have good days and not-so-good days, but I'm thinking that, at some point, either dramatically or otherwise, the not-so-good will far outweigh the good. Has anyone out there experienced the same situation with their loved one? I appreciate any feedback you can provide.