Let sleeping Elves lie?
 

It is said that the Quendi require little or no rest. Why, then, was each member of the Fellowship required to keep watch at night during their journey through Moria?

(or did Legolas always assist in the watch?)

During Aragorn, Gimli and Legolas' chase after the Orcs who seized Merry and Pippin, Legolas comments that "the green smell" is "better than much sleep". Later it is said that "Legolas was first afoot, if indeed he had ever slept..." These quotes have led some to believe that Elves do not sleep or need little sleep. In the Hobbit, Galion falls asleep after drinking too much wine. It seems Elves do sleep, though they may not require as much as men. Keep in mind that the bodies of Elves and Men are fundamentally the same; it is the strength of the link between body and spirit that makes men mortal and Elves nearly immortal (HoME 10). Thus Elven bodies must tire and occaisionally require sleep.

I guess there is not much nice 'green smell' in Moria. My guess is that Legolas couldn't relax, and thus rest while awake, in Moria, because of the lack of good living things and the constant threaths.

Jellinek

I have read that they do not have to sleep, only to dream or fill thier eyes with beutiful things. Just a guess. They dont seem to tire very fast.