Ever post something online or even buy something on your phone and don't remember? Maybe you were in Microsleep - a dangerous phenomenon where parts of the brain are still active, and others are in sleep mode.
Experts say during microsleep your eyes can still be open and you can still carry out tasks, almost like you're on auto pilot.
The driver of Sunday's deadly train derailment in New York says he felt like he was in a daze, moments before the crash. Some experts think he may have experienced microsleep.