We do meditation to relax and feel energetic.
meditation means control over mind to stop unwanted thoughts generating in mind.
But during meditation if according to theory we stop all thoughts generating in mind, then brain will sleep.
That is,
Sleeping is a process in which their are No inputs from our 5 sensory organs,
as meditation process also off's the inputs from sensory organs then person should immediately sleep.
But some do this without sleeping,
That's why meditation is not science but a feeling which cannot be written in steps.
That's why we wouldn't say that meditation is simply sleeping process.