- Semantic and technical distinction between circadian cycle and sleep.
Is, in biology, the notion of the circadian cycle (or rhythm) that one finds also in elementary forms of life (say a paramecium) the same notion of "sleep"? If not what is its technically difference? If it is, why are then biologist surprised to observed sleep-like states in organism with primitive nervous organization like in the freshwater polyps? https://pubmed.ncbi.nlm.nih.gov/33028524/