To answer this question, I think it is important to appreciate the following important aspect of Alzheimer's disease; most patients with Alzheimer's disease also have other medical conditions that can
contribute to impaired thinking. This means that the patient's memory, judgment, and verbal abilities may be diminished by a combination of effects from Alzheimer's disease and from other conditions.
If an Alzheimer's patient demonstrates a sudden improvement, it usually indicates that something has changed. It might be some aspect of the patient's environment has improved, for example a relationship or housing arrangement, or it might mean, that some other medical condition has been resolved.
A partial list of common medical conditions known to impair thinking includes:
diabetes, anxiety,drug use (prescription as well as over the counter), small silent strokes, depression, urinary tract infection, thyroid imbalance, and vitamin B12 deficiency.
In some instances, fluctuations in memory and verbal abilities do precede further decline but it really depends on what is causing the fluctuation. I am not aware of any evidence suggesting that Alzheimer's disease, as it is currently understood, goes into remission. It seems to advance progressively, albeit at different rates with different people, and is not known to reverse course.