Lakshman did not sleep for the entire period of 14 years to protect his brother Ram and sister- in-law and Sita.

Urmila asked Nidra, the goddess of sleep, to take away all of Lakshmana’s sleep for the fourteen years of exile, so that he could remain awake and ever attentive to Rama and Sita’s needs. She remained asleep throughout the fourteen years, waking up to see Rama’s coronation when Lakshmana returned to Ayodhya and relieves her of her duties.

source: http://en.wikipedia.org/wiki/Urmila_(Ramayana)