Full context:   Difficult experiences encountered in meditation are mentioned in traditional sources; and some may be considered to be an expected part of the process, e.g., seven stages of purification mentioned in Theravāda Buddhism. Possible "unwholesome or frightening visions" are mentioned in a practical manual on vipassanā meditation. Classical sources have various terms for "meditation sickness" and related difficulties, such as zouhuorumo (走火入魔; 'fire possession'), chanbing (禪病; 'Chan disease') and mojing (魔境; 'demonic states').