How effective is lying down with eyes closed as a substitute for sleep? Resting, as opposed to sleeping, helps with physical recovery and relaxation, but much of the benefit of real sleep is mental.

If I can't sleep, how much, if any, sleep-related benefit is gained by lying down for 6 hours with my eyes closed?
I believe the important⁽¹⁾ point is paradoxical sleep. If you cannot sleep, you should try to defocus your thought, in order to allow neurones to "run freely"⁽²⁾.

(1) It has be shown that rats deprived of paradoxical sleep died in 16-54 day.

(2) I don't know if this will work, but I've been taught at university that neurons can die from sub or over stimulation. For this reason I've come to the conclusion that one of the objectives of dreaming is to allow neurons to fire action potentials in regards with their own physiological needs, instead of coordinated thoughts needs of the brain.