1. A method of detecting sag in a drilling fluid within a borehole, the method comprising: (A) measuring a first pressure with a first sensor positioned at a point within the borehole, the first pressure being measured at a first time following cessation of a flow of the drilling fluid within the borehole; (B) measuring a second pressure with the first sensor at the point within the borehole and at a second time following cessation of the flow of the drilling fluid; (C) determining a first theoretical pressure and a second theoretical pressure at the first and second times, respectively, at the point based on a computer model that includes known dimensions and features of the borehole at the point and a current composition of the drilling fluid; (D) calculating a theoretical pressure slope between the first theoretical pressure and the second theoretical pressure; (E) receiving the first and second pressures with a processor communicatively coupled to the first sensor and calculating a pressure drop based on the first and second pressures; and (F) comparing the pressure drop and the theoretical pressure slope using the processor to a threshold indicating sag such that: when the pressure drop and the theoretical pressure slope does not exceed the threshold indicating sag, repeating the (A)-(F) steps until the threshold indicating sag is exceeded; and when the pressure drop and the theoretical pressure slope exceed the threshold indicating sag, undertaking at least one corrective action selected from the group consisting of adding a modifier to the drilling fluid, changing a rate of rotation of a drill string, restarting flow of the drilling fluid, pumping the drilling fluid while moving the drill string, and any combination thereof.