Like their forerunners, post-Hellenistic doctors also grappled with the unclear boundaries between healthy versus pathologic sleep, and consciousness-unconsciousness. Furthermore, they incorporated new diseases and redefined others - like lethargy - that were specifically associated with this process. Celsus considered sleep as all-or-nothing phenomenon, without recognising different depths. Regarding mental capacities, he subsumed most of them in his idea of mens/animus. Aretaeus, on the other hand did conceive different depths of sleep, and his eclectic method enabled him to find alternative pathophysiological explanations to characterise several of its main features. Similarly, although his organization of mental capacities varied according to what he was explaining, the opposition gnômê-aisthêsis was important in his idea of mind.

Galen conceived sleep and wakefulness as a continuum that depended on the mixture of qualities within the ruling part of the puschê (the hêgemonikon) located in the brain. Naturally, in his system whenever pathological sleep occurred the doctor needed to determine if the brain was affected directly or by sympathy (from another organ), and the precise imbalance of qualities that needed to be counteracted by their opposites. His idea of mind was very accurately and hierarchically structured: it resided in the logical part of the soul, located in the brain, and several diseases with impaired consciousness compromised its normal functioning.