tamburina:

The thousand-yard stare or two-thousand-yard stare is a phrase originally coined to describe the limp, unfocused gaze of a battle-weary warrior. The stare is a characteristic of acute stress reaction, also known as combat stress reaction, which is related to post-traumatic stress disorder. The despondent stare is a symptom displayed by victims who have succumbed to the shock of trauma by dissociating from it. The phrase originated from military circumstances, but it is a symptom of severe psychological distress that can occur anywhere and is not unique to soldiers or settings of warfare.

Photo: Wounded soldiers during World War I. The soldier in the lower left is exhibiting the thousand-yard stare.