<prompt> Not true about nocturnal penile tumescence is -Totals about 100 min nightNormal phenomenonOccurs in NREM sleepCan be used to distinguish between psychological or organic impotence  <response>: Nocturnal penile tumescence occurs in REM sleep. It is a normal phenomenon and occurs for 80-120 minutes per night. It can differentiate psychogenic impotence from organic impotence. 