Lakshman did not sleep for the entire period of the exile of 14 years in order to protect his brother and sister- in-law Rama and Sita. Because of this he is called as Gudakesh. When the goddess of sleep appeared before him at the first night of the their exile to the forests and when Rama and Sita were asleep, Lakshman requested the goddess to give him no sleep for the entire 14 years, so that he can be awake to protect his beloved brother and Sita. The goddess was impressed by this and granted the boon on a condition that someone else have to bear his sleep. On Lakshman request the goddess visited his wife Urmila, sister of Sita. Urmila agreed to share her husband loss of sleep, and thus slept for entire 14 years. Hence the reason she is not much in the story, but a strong reason for helping Laksman to kill Ravana son Meghnadh in the war against to Ravana as Meghnadh could be killed only by a man who have not slept for 14 years.