Crashing has to do with saturation. At high tempurates, a solution can hold at higher concentrations. As the temp falls and time goes on, the solution becomes supersaturated. As in, its beyond its saturation point for that stp. It might actually hold at this mg/ml, but the further from its saturation point and the longer it sits, the more it wants to come out of solution. In the case of hormones, it will usually, if not always, crash out of solution in the form of crystals. Btw, this is how rock candy is made. Same prinicple.