The Economist worries about deflation, specifically in the Euro area. The central passages are:

Central bankers can no longer set real (that is, inflation-adjusted) interest rates low enough to restore demand. Wages, incomes and tax revenue all stall, undermining the ability of households, businesses and governments to pay their debts—debts which, in real terms, will grow more burdensome under deflation.

… bad deflation results when demand runs chronically below the economy’s capacity to supply goods and services, leaving an output gap. That prompts firms to cut prices and wages; that weakens demand further. Debt aggravates the cycle: as prices and incomes fall, the real value of debts rise, forcing borrowers to cut spending to pay down their debts, which ends up making matters worse.