Rest = Alertness
Before the discussion of yoga and meditation in various journals, rest and alertness were taken as opposite. Since researchers have been enormously finding facts associated with yoga and other religious scriptures, it was noticed and later, accepted that the two states are not opposite, rather they can coexist in yoga and meditation or other similar practices.
Alertness may not coexist with rest in any other state but the effects of yoga has come out as a challenge from recent decades to find other hidden theories and experiments performed by yogis of ancient era. Hath yoga is a great practice usually performed to purify one's inner soul by removing diseases of physical structure and discomfort of psychic structure to make complete balance of mind-body and soul.