be on automatic pilot

be on ˌautomatic ˈpilot

do something without thinking because you have done the same thing many times before: I got up and dressed on automatic pilot.
The automatic pilot is the device in an aircraft that keeps it on a fixed course without the need for a person to control it. It is often shortened to ‘autopilot’: I did the journey on autopilot.
See also: automatic, on, pilot