The cold conditions resulted in : ( i ) higher MBPS than under warm conditions ; ( ii ) significant and greater sympathetic index changes during the sleep-wake transition than during cover-to-uncover and supine-to-sit position tests ; ( iii ) the non-REM-REM transition-related sympathetic elevation during the cold conditions being significantly higher in late sleep period than in early sleep period ; ( iv ) at 1h prior to morning awakening , the value of total power of heart rate variability changes being significantly negatively correlated with the changes of near-body temperature ; and ( v ) significantly higher arousal index and shorter average interval of REM periods than in warm conditions .