Imagine yourself taking a nap. A few hours is fine. A good night's sleep can be refreshing. But at some point a nap becomes a coma. In much the same way, deflation can be a thoroughly positive phenomenon in its most benign form.
Lower prices mean consumers have more spending power.
As long as consumption stays healthy, deflation represents a windfall to buyers. However, falling prices for goods and services can indicate serious problems. They may suggest slack demand, which ripples through an entire economy and begins a downward spiral. That is what set off sky-high unemployment and serious deflation during the American Great Depression of the 1930s. If consumers stop buying, corporate profits decline.