Around 5 am, most people are in lighter stage of sleep, so getting up feels more refreshing. Air is cooler and quieter, supporting calm 'rest-and-restore' response, said Saurabh Bothra, co-founder, Habuild. However, Dr Swarup Swaraj Pal, Chief CVTS surgeon, Gleneagles Hospital, said nervous system functions best when it gets restorative sleep regardless of whether one wakes up earlier or later.