I don’t know what the politically accurate terms are for the intellectually challenged or the mentally ill. I ask your forgiveness if I have misused terms; if I’ve said something insulting, it is a result of my ignorance, not my design. For terms used in historical context, please keep in mind that in the Middle Ages, these terms were merely descriptive and only became derogatory over time.
Medieval man distinguished between those who had mental challenges from birth and those who developed them later, either from physical injury, “evil spirits,” or various forms of trauma. In deciding a person’s diagnosis and responsibility, attention was given to whether a person had lucid intervals or was continually of unsound mind.
natural/congenital idiot: This was a person who was “incompetent from birth.” He was placed in the wardship system; his protector would oversee his care and maintain his property until his death, when the lands would pass to his next of kin. 
lunatic: This was a person who had become “incompetent” during the course of his life. He was not cared for under the wardship system. Sometimes the king or lord would oversee his lands, but care was a family issue, and a person deemed a lunatic could still own property, which he would maintain during his lucid periods. 
From the late 13th C, “congenital idiots” were protected by law.  Care of “lunatics” was the family’s responsibility, but if the family could not or would not provide for them, the government would step in.  Care for the intellectually challenged was considered a community responsibility. 
Popular imagination usually assumes that treatment of the mentally ill in the Middle Ages would be ineffective and undignified, at best. C.H. Talbot argues that
“The general assumption seems to be that the Middle Ages was far more brutal in [treatment of psychological cases] than we are today and that mental patients were bound with thongs, flogged, put into irons, thrown into noisome prisons and dungeons or even executed as felons. It may come as a surprise to learn that this was by no means the case. The law in England, at least from the thirteenth century onwards, was not very different from what it is today, and the treatment meted out to the offenders was mild, reasonable and compassionate.” 
Medieval men and women were not idiots (modern use). They observed frequently that the mental faculties were disrupted by a blow to the head or fever. They observed that some people had diminished mental faculties from birth. Cruel treatment of such a person would no more be permissible than cruel treatment of children, the elderly, or the infirm.
A person’s incapacity was determined through inquisition, and thus no inquisition was valid unless the subject was interviewed in person.  Nobody could have his neighbor thrown into prison or have his lands confiscated by simply accusing him of madness. Questions to verify incapacity were generally common sense and included “memory tests, simple skills, and general knowledge.”  Some recorded questions are identical to the ones patients are immediately asked today in cases of head trauma—what is today’s date? What are your parents’ names? However, a formal process of inquisition was usually necessary only when the subject owned land and thus needed the legal system to assure fair maintenance.  If legal property is not in jeopardy, there is no need for a legal verification of incapacity, as it did not decide the person’s care.
Medieval art and stories frequently depict madness being cured by saintly intercession. This does not reflect the norm from historical records and likely is intended to teach something about the saint, not about the patient. By the 14th C, insanity brought by trauma or fever was widely understood.  While humorism influenced medieval treatments, medieval society recognized a range of psychological issues and “commonsense attitudes to insanity were widespread.”  Charms and incantations were frequently used by the uneducated for treatment of permanent conditions, but dietary and herbal treatments were also common and most likely to be used by doctors.  Medieval man understood a physical cause for mental disorders and thus did not need to resort only to the supernatural for healing.
England did not have any institutions specifically allocated for mental patients. However, St. Mary Bethlem (Bedlam), a hospital established in 1247, was converted to a mental hospital at the end of the 14th C.  Records show that this hospital had “fetters, irons and stocks” that were used on the patients. However, records also show that patients were allowed to walk about at their will. C.H. Talbot insists that records prove restraints were only used when patients were violent and were removed once the paroxysm ended.  Records of donations to St. Mary Bethlem show a desire from both the doctors and their patrons to “provide whatever medical and scientific means were available at that time for the benefit of the insane,”  thus showing that such people were not regularly abused or treated only as an embarrassment to be hidden away.
On the whole, the perception of the mentally challenged in the Middle Ages was “kindly and tolerant, full of compassion rather than of criticism, based on the realization that mental disturbance was often the outcome of emotional upset and resulted in diminished responsibility.”  Of course, this doesn’t mean you won’t find instances of the mentally disabled being abused or taken advantage of. However, this was not the norm, nor was it allowable. As always, consider the difference between the actions of good and bad men.
Both history books meant to be riveting and student research papers tend to latch onto demonic possession as the main cause medieval man would claim for mental instability: “In the popular mind the Middle Ages was a period of unreason in which belief in possession was a commonplace, and indeed the perception has coloured many scholarly examinations of insanity in former centuries.”  There is little evidence that demonic possession was routinely blamed for any mental condition save epilepsy.  I find references to the influence of “evil spirits” used most often when the afflicted has committed a crime or done violence during an episode, and this term seems to refer to the gravity of the case rather than a literal belief in evil spiritual influence.
- Roffe, David, and Christina Roffe, “Madness and Care in the Community: A Medieval Perspective,” BMJ: British Medical Journal, 311.7021 (1995): 1709.
- Ibid., 1708.
- Talbot, C.H. Medicine in Medieval England (London: Oldbourne, 1967), 180. This passage uses the word “offenders” because it focuses on cases where a crime had been committed and led to the question of diminished responsibility.
- Roffe, “Madness,” 1710.
- Ibid., 1709.
- Talbot, Medicine, 183.
- Ibid., 184.
- Ibid., 185.
- Roffe, “Madness,” 1708.
- Ibid., 1709.