This has only happened to me two times so far. My S3-LTE watch has slipped into Power Reserve mode after I have taken my watch off and placed it on the counter for about 20 minutes. When I grabbed my watch to put it back on, I noticed it had switched to Power Reserve mode. When I pressed the side button to bring it back to life, I have 96% battery life remaining so I don't think it's because my watch ran out of battery. Has anyone else noticed this behavior?