jagrhus tad-visrstam tam

 jrmbhanakhyam tanum prabhoh

nidram indriya-vikledo

 yaya bhutesu drsyate

yenocchistan dharsayanti

 tam unmadam pracaksate

 

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 

 

The ghosts and hobgoblins took possession of the body thrown off in the form of yawning by Brahma, the creator of the living entities. This is also known as the sleep which causes drooling. The hobgoblins and ghosts attack men who are impure, and their attack is spoken of as insanity.

 

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 

 

The disease of insanity or being haunted by ghosts takes place in an unclean state of existence. Here it is clearly stated that when a man is fast asleep and saliva flows from his mouth and he remains unclean, ghosts then take advantage of his unclean state and haunt his body. In other words, those who drool while sleeping are considered unclean and are subject to be haunted by ghosts or to go insane.