How did the Aztecs deal with mental illness?

This is an excellent question, but also a huge one! Here we can only hint at the extent of Mexica knowledge and awareness of human psychological problems and of the range of methods they used to tackle these. Whilst the Aztecs may not have analysed them in Western terms, there can be no doubt that they treated mental conditions and disorders using therapeutic remedies ranging from herbal medicines and incense offerings to ‘logotherapy’ (talking it through, to you and me) and bathing, and from bloodletting to ablutions and suction. Central to their approach was the idea of illnesses being caused by a combination of external as well as internal factors. There are several Nahua terms referring to the idea of ‘possession’, often implicating a foreign entity that has entered a person’s being.
’The two kinds of dangerous aspects most mentioned in the sources as causing pathological intrusions are the mocihuaquetzque or cihuapipiltin and the minor rain gods. Madness and various kinds of paralysis are attributed to the former... The most characteristic sickness, thought be a possession by the rain beings, was a kind of madness mingled with evil in a single pathological process, having its origin in a lightning bolt.’ (López Austin). The cure was a herb called ‘medicine for aquatic fever’.

Pic 1: The concept of ‘possession by supernatural spirits’ was a common diagnosis for Aztec healers; detail of mural by Antonio González Orozco, Hospital de Jesús Nazareno, Mexico City

Mental stupor was equally believed to be due to an excess of phlegm in the chest, and could be treated with herbs to induce vomiting, such as yolloxochitl (‘heart-flower’ - pic 3). One particular herbal medicine ‘applied locally to the head, helps the frenetic and crazy, removes fear... returns to consciousness [those] who have lost consciousness for any reason’. Significantly, we find a whole plethora of terms relating to conditions of the heart - but these are not physical conditions, they’re psychological or spiritual: hearts being ‘eaten’ (by bad spirits), ‘squeezed’, ‘congested’, ‘crushed’, ‘spinning around’, ‘wanting to die’...
Medicines made of herbs, flowers and crushed stones were complemented by non-invasive therapies we still use today, including ‘ritual language’, the relieving and releasing of suppressed emotions by encouraging the sufferer to talk about the issue (catharsis) and a generally benign human relationship between healer and patient that included the involvement of family and local community (a principle only acknowledged in the West in the 1970s). When we speak of psychotherapy and talk therapy, we’re recommending techniques already in use by the Mexica centuries ago!

Pic 3: ‘Heart-flower’ (right), the roots of which should be crushed in water and given to sufferers of mental stupor - just part of the recipe from the Badianus Manuscript, plate 98

Sources:-
• The Human Body and Ideology: Concepts of the Ancient Nahuas by Alfredo López Austin, translated by Thelma Ortiz de Montellano and Bernard Ortiz de Montellano, vol. I, (University of Utah Press, Salt Lake City, 1988)
• The Badianus Manuscript/’An Aztec Herbal of 1552’, facsimile edition (The John Hopkins Press, Baltimore, 1940)
• Aztec Medicine, Health and Nutrition by Bernard Ortiz de Montellano (Rutgers University Press, 1990)
• The Natural History of the Soul in Ancient Mexico by Jill L. McKeever Furst (Yale University Press, 1995)
• Encyclopedia of American Indian Contributions to the World by Emory Dean Keoke and Kay Marie Porterfield (Facts on File, 2002).

Pic 5: Stone Cihuateteo statue, National Museum of Anthropology, Mexico City