Perhaps of interest to you, Pamela Pattison Lash, genealogist extraordinaire of Williams County, Ohio, fame, has some interest in the topic of insanity/mental illness in the 1800s, with a special interest in women and these conditions. You might want to contact her to learn if she knows others engaged in research about this. She blogs at "Williams County, Ohio Genealogy." She's blogged some on the topic. "Sensitive Subject--Insanity in Williams County, Ohio"; "Old newspaper--Sad account of "Wife of Andrew Svoboda, 1904."
A couple of general references follow; these may be less specific than you would like:
"A Glossary of Archaic Medial Terms, Diseases and Causes of Death," Rudy's List of Archaic Medical Terms (http://www.antiquusmorbus.com/Index.htm ); entry for "insanity," "Persistent mental disorder or derangement. No longer in scientific use; cites W. B. Saunders, Dorland's Illustrated Medical Dictionary, 2002.
"Some medical terms used in old records," Michigan Family History Network, entry for "Mania or Acute Mania," including comment that it was defined as "severe insanity"; says "Acute Mania was used as a term for death when the patient had been hospitalized..."
Perhaps someone will be able to find data that is more timely (to 1872) or more regionally relevant (Minnesota), but I did find some interesting information.
Washington (state), Third Biennial Report of the Board of Trustees of the Eastern Washington Hospital for the Insane ... (Olympia, Wash: O. C. White, state printer, 1896)
- p. 19-22, Tables 6-7, "Alleged Causes of mental disorder ..." (Child bearing is one of the conditions listed."
- p. 22, Table 9 for "Forms of mental disorder in patients admitted, recovered and died ..."
- p. 23, Table 10, "Cause of death of patients admitted ..." Many of these are common causes of death of the day; any number are listed as "Exhaustion from ..." There are other listings you may want to research further.
Statistics of the the United States (including mortality ...) in 1860; compiled from the original returns and being the final exhibit of the [1860 U.S. census] ... (Washington: Government Printing Office, 1866), p. 343 for "Mortality of the United States. "Insanity was stated to be the cause of death if 300 in 1850 and 452 in 1860, in all the states ... The proportion was twice as great in New England and New York as in Michigan, Wisconsin, Minnesota, and Nebraska ... The large proportion of insanity in California is produced by the excitement and oppressive anxieties, and the great and sudden changes of fortune among many of the people."
Also, a report by the Rhode Island Registrar of Vital Statistics, including p. 236, a table reporting the "Mortality in the State from Insanity, 1866 to 1903, inclusive."
Although I did not much review this material, it might provide even more detail on the topic, thought also from a later time. See, Henry C. Chapman, M.D., A manual of Medical Jurisprudence: Insanity and Toxicology (Philadelphia: W. B. Saunders & Company, 1903).