Lud-In-The-Mist by Hope Mirrlees — Read

There were days, however, when even the silent things did not soothe Master Nathaniel; when the condition described by Ranulph as the imprisoning of all one's being into a space as narrow as a tooth, whence it irradiates waves of agony, became so overwhelming, that he was unconscious of the external world.

One late afternoon, a prey to this mood, he was mooning about the Fields of Grammary.