Healthcare insurance giant UnitedHealth Group (UNH -11.14%) has seen its stock go from a stable stalwart to a falling knife, seemingly overnight. The stock's price crashed 22.4% on April 17 in response to its first-quarter earnings results and full-year guidance cut. Then on Tuesday, UnitedHealth fell 17.8% in a single session after its CEO stepped down and the company removed its full-year guidance.The sell-off has pushed shares of UnitedHealth down to around their lowest level in five years. The dividend ...