I feel like this article touches a lot more on the definition of what sleep is, rather than what people commonly refer to as sleep. I mean, what really defines

I feel like this article touches a lot more on the definition of what sleep is, rather than what people commonly refer to as sleep. I mean, what really defines sleep? I would've thought it is the temporary absence of consciousness in an otherwise conscious being. Or something along those lines. Of course that wouldn't make a lot of sense with medical comas and such. So maybe sleep is just a, perhaps regular, phase in which an organism is 'inactive', that is, doesn't perform a lot of actions or waste energy. Energy is limited after all. From an evolutionary perspective, it might make sense to have an organism not be dependent on a permanently available power source. It'd be better to alternate between using a lot of energy and using less energy, because permanent sources of energy are rare or even non-existing. Depending on such a permanent source would starve the organism to death and hence it wouldn't evolve. So you get those intervals and they'll naturally evolve to synchronize to the phases of their energy source. And that's supposedly the sleep cycle?