There is no remissness in sleep, it is only when one is awake that there is remissness when you delay saying the prayer till the time for the next prayer comes.
قَالَ رَسُولُ اللَّهِ ﷺ لَيْسَ فِي النَّوْمِ تَفْرِيطٌ إِنَّمَا التَّفْرِيطُ فِي الْيَقَظَةِ أَنْ تُؤَخَّرَ صَلاَةٌ حَتَّى يَدْخُلَ وَقْتُ أُخْرَى