Still in the context of the discussion of bikur holim our Gemara mentions some of the repercussions of illness. The Gemara brings Rav Yosef’s warning that someone who becomes ill can forget his learning, and then reports that Rav Yosef himself forgot his learning after a serious illness, and it was his student, Abaye, who took it upon himself to remind Rav Yosef of his previous teachings. The Iyun Ya’akov suggests that Rav Yosef’s example is a particularly powerful one since Rav Yosef is known in the Gemara by the soubriquet “Sinai,” implying that he had a vast store of knowledge and knew all that was taught on Mount Sinai.
The Gemara continues with the story of Rabbi Yehuda HaNasi, who developed thirteen different approaches to every halakha and shared seven of them with his student, Rabbi Ḥiyya. When Rabbi Yehuda HaNasi became ill and forgot his teachings, Rabbi Hiyya successfully reminded him of those approaches that he had learned. It turned out that a certain laundryman had overheard Rabbi Yehuda HaNasi while he was developing his approaches and was able to share them with Rabbi Ḥiyya, who was then able to re-teach them to Rabbi Yehuda HaNasi. The Gemara records that when Rabbi Yehuda HaNasi met the laundryman again, he credited him with having reestablished these teachings.
Rav Sherira Ga’on explains that Rabbi Yehuda HaNasi’s “approaches” were essentially the different versions of oral traditions that were brought before him. Rabbi Yehuda HaNasi’s success was in clarifying each of these versions and editing them into the work that we know as the Mishna.
There are a number of different illnesses that directly affect the brain itself – aneurisms, meningitis, etc. Such diseases are likely to cause severe damage to brain function, to the extent that even total amnesia may result. Other diseases, too, may cause similar damage, even though they are not connected directly with the brain. Measles, for example, or whooping cough, can also cause brain damage. Such situations can cause damage to the sensory centers and even to thinking and recognition, which can bring about partial or total memory loss.