Theory 1:Gremlns-The scale gremlins sneak in each night and secretly change your scale up or down... depending on their mood for the day. (lol)

Theory 2:Evaporation - The food you've ingested is modified to liquid in the body and you sweat it out overnight due to erotic dreams and/or being chased by monsters...or was it monsters that want sex?? (lol)

Theory 3:Gas- Your body has pent up enormous amounts of toxic gasses from that bean burrito you snarfed down for lunch or dinner. At night (only), you let out enough gas to fill the hindenburg blimp. Unfortunately, the only evidence for this theory is a sore bum or dead plants/animals in the immediate area. (lol)