 In human infants sleep develops rapidly during early development.This development includes an increase in non-rapid eye movement sleep (NREM sleep) which is also called quiet sleep (QS) during the first 12 months of life in association with a decrease in rapid eye movement sleep (REM sleep) which is also known as active sleep (AS).In addition, slow wave sleep (SWS) which consists of stage 3 and stage 4 NREM sleep appears at 2 months of age and it is theorized that some infants have a brain-stem defect which increases their risk of being unable to arouse from SWS (also called deep sleep) and therefore have an increased risk of SIDS due to their decreased ability to arouse from SWS.