Lakshmana requested the Goddess of sleep (Nindra) to go to his wife Urmila. As he would not sleep for 14 years. He will stay awake day-night and watch for dangers in the forest while his elder brother and sister-in-law sleep in peace.
Urmila in return accepts her husband’s dedication towards his elder brother and agrees to sleep for 14 years. At night she would sleep for her and in the day she would sleep on-behalf of her husband.