I am glad to read your question because I have wondered that myself. I have read some interesting journal articles about sleep in persons with PD. I have seen some conceptual answers but nothing definitive that explains "why" tremors might stop. They tend to describe what occurs during the sleep cycle by studying persons with PD during sleep. Some authors describe a reduction in tremor amplitude or cessation of tremor that lasts until later in the sleep stage cycle or upon waking. I will keep reading and hope you will post if you find some helpful information. Regardless of the reason, I am glad that medication and sleep (when it comes) stop my tremors. Kind regards, Lorraine, ParkinsonsDisease.net moderator.