ZONE OUT (Slang): To lose all concentration; to slip out of normal consciousness, and have nothing on your mind. Etymology: A 'zone' is an area or place. If you 'zone out', you mentally drift away from the place you are currently, and go off into empty, dreamy space.
"After working on a document for four hours straight, I zoned out in front of my computer screen."
Synonym: SPACE OUT: "I always space out when life gets boring." "I tend to space out... but more so now than lately. " "Tune in, turn on, space out."