Meditation and yoga (yes, they are seperate), have great beneficial effects on the body and mind, but in no way are they an alternative to sleep. As mentioned above, the body needs time to prepare itself for another day of working and living the life we have put ourselves into. Both meditation and yoga teaches the mind to stay focused, which in turn, allows us to take an outside perspective on everything in our life, and see a much brighter light than others. That's the basic form of meditation. It can later be taken to great lengths in becoming one with the Divine, and opening up, and clearing blocked chakras, the major energy centres of our body. But even with that, nothing comes close to the benefits of having a full rest. Full usually being 8 hours, as dictated by science.Meditation does help make us feel more awake afterwards (considering you have grounded properly), but only for a short time.All in all, meditation and yoga is best used in balance and conjunction with proper sleep. And I wouldn't recommend doing anything other than that, for your body's sake.