Origin of the word "Lethargy"

The word "lethargy" comes from Greek mythology and is connected to the River Lethe, one of the five rivers of the Underworld .

In Greek mythology, when souls entered the Underworld after death they had to cross the River Lethe. This river was known as the "River of Forgetfulness." Anyone who drank its waters would forget their past life—their memories, joys, sorrows, and even their identity.

The goddess Lethe was the personification of this river and forgetfulness itself. Drinking from Lethe was essential for souls who were to be reincarnated. They needed to forget their previous lives before starting anew. However, for those who remained in the Underworld  this forgetfulness symbolized eternal oblivion—a state of deep sleep or unawareness.

The Greek word "lēthargos"  comes from "lēthē"  meaning forgetfulness, and "argós" meaning idle or inactive. Over time, "lethargy" in English came to mean a state of extreme drowsiness, tiredness, or lack of energy, much like the souls who forgot everything and lost their awareness in the Underworld.

In simple terms, "lethargy" comes from the idea of forgetfulness, sleepiness, and inactivity, just like the souls who drank from the River Lethe and lost all memory of their past.