The change most Spartans comment on after waking from augmentation is a reduced need for sleep. You may only feel the need to rest for two hours a day (a feeling that comes more from routine than anything else).

Spartan Field Manual Pg 38

	Spartan-IV-class operatives can expect to perform optimally with a minimum of two-and-one-half hours of sleep per forty-eight (48) hour cycle.

Infinity Briefing Packet