in a fog
Also, in a haze. Preoccupied, not paying attention; also, at a loss, confused. For example, After the accident he went about in a fog, even though he had not been injured, or Millie always seems to be in a haze; she never knows what's going on. These expressions allude to fog or haze obscuring one's view; the fog usage dates from about 1600, haze from about 1800.
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