The middle part of the night, after the first REM episode, begins with another period of non-REM sleep followed by another arousal and a longer and more intense REM episode. Throughout this part of the night, usually lasting about four hours, the child alternates between progressively longer and more intense periods of REM and relatively light periods of non-REM sleep. It is during these hours of light sleep, particularly at the transitions between REM and non-REM sleep, that wakings are most common.
