Yes, dementia can appear to worsen suddenly, and when this happens it is usually a sign that something else is going on rather than a natural progression of the disease itself. A urinary tract infection is the most common culprit and can cause rapid and dramatic changes in behaviour, confusion, and cognitive function. Other causes of sudden deterioration include dehydration, new medications or medication interactions, a fall, an acute illness, constipation, or a significant change in environment. This type of sudden change is called delirium superimposed on dementia. Treating the underlying cause can often lead to a return to the person’s previous level of functioning.