Losing your phone is a stressful experience. Take a deep breath and use the tools built into Android to track down your phone.
It happens in the blink of an eye. You place your phone down on a counter at the cash register or feel a slight bump as you get off the subway, only to later realize your phone is gone. Regardless of how you lose it, be it from theft or a simple mistake, losing your phone is a stressful experience.