Galen system is based on three pillars: the affected body part, the type of qualities imbalanced, and the degree of imbalance. Therefore, he only distinguishes between mental illness and impaired consciousness when there is a difference between these two entities in any of these three pillars. Thus, he distinguishes phrenitis from melancholia but not from mania. The emphasis on the system, on the other hand, enables him a very tight notion of disease, where symptoms, mechanisms, affected organ and treatment are closely linked.

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.

4 Post-Hellenistic authors present a more compartmentalised idea of diseases in general and of impaired consciousness in particular. Unlike the Hippocratics, who barely discussed mental illness, these authors did distinguish impaired consciousness from mental illness through a classificatory system of dichotomic oppositions, additionally they discussed new conditions which are not mentioned in the HC. In most theorisations, perceptions play an increasingly relevant role to understand these conditions.

In the Introduction I set out to explore accounts of impaired consciousness in ancient medical texts through two axes. In the longitudinal thematic one, I aimed to contrast the different approaches to the topic against their respective medical contexts, and to establish relationships between texts, authors and periods. The transversal axis, on the other hand, focused on how the development of ideas and debates around impaired consciousness illuminates our understanding of other concepts about ancient medicine in general, and about the alluded to authors in particular. In summarising the main findings of this research I will first focus on the transversal axis, and then I shall add my final remarks about impaired consciousness itself.

Hippocratic doctors discussed two forms of total loss of consciousness. The most common one, where they equated fainting with a separation of the soul, and another form - independent from the psuchê - where they saw the concurrence of numerous independent bodily symptoms that ended up in a swoon. The momentary disruption of cognitive functions that occurred during fainting, and their definite cessation with death made them conceive the soul as both a broad notion that subsumed numerous mental capacities (which transiently separated from the body during swoons) and as a life force that abandoned the body for good with death.

Some Hippocratic doctors regarded sleep as a healthy process, and some as a pathological one; some of them struggled to distinguish between hallucinations and nightmares, and some between deep dreamless sleep and total loss of consciousness. This chapter explores how different treatises from the Hippocratic corpus navigated these ambiguities, how they explained different depth of sleep (i.e. different levels of consciousness), and how such understanding relates to their views on mental capacities (which they subsumed in concepts such as phronesis, sunesis, gnômê, and nous).

A diachronic look at the contrast between mental illness and impaired consciousness among these ancient doctors shows a trend towards a more compartmentalised idea of these conditions, a stronger notion of disease, and a progressive abstract framing of clinical findings into theoretical classificatory models and comprehensive pathophysiological systems.

This introductory chapter presents and contextualises the main sources under study, and addresses the problems of a definition of consciousness. Given the vagueness of the notion, a working definition is proposed, which is based on cognitive model that uses three prototypical clinical presentations of impaired consciousness: delirium, sleep and fainting.