Hallucinogen persisting perception disorder (HPPD) is a chronic (and sometimes permanent) disorder in which a person has flashbacks of visual hallucinations or distortions experienced during a previous hallucinogenic drug experience, usually lacking the same feelings of mental intoxication experienced before. Hallucinations are usually not intense or impairing and consist of visual snow, trails and after images (Palinopsia), light fractals on flat surfaces, intensified colors or other psychedelic visuals. To be diagnosed, the disorder must cause distress or impairment in work or everyday life. The flashbacks may be continuous or just occasional. Symptoms often get worse when focused on.