automatic pilot

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A navigation mechanism, as on an aircraft, that automatically maintains a preset course.
• noun A state of mind in which one acts without deliberate effort or self-awareness.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a navigational device that automatically keeps ships or planes or spacecraft on a steady course
• noun a cognitive state in which you act without self-awareness