There have been instances in which saying that a major stock fell off a cliff, as when describing the fortunes of UnitedHealth (NYSE: UNH) in the Thursday pre-market, and immediately after the morning bell.Specifically, in the first hour of the trading day, UNH stock dropped 19.17% to its press time price of $472.91, resulting in a total decline of 20.51% in the weekly chart.UNH stock one-week price chart. Source: FinboldUnitedHealth’s latest earnings report, published early on Thursday morning, April 17, i ...