"loss of memory," 1786 (as a Greek word in English from 1670s), Modern Latin, from Greek amnesia "forgetfulness," from a- "not" (see a- (3)) + mnesi- "remembering" (found only in compounds), from stem of mnasthai "to recall, remember," which is related to mnemnon "mindful," mneme "memory" (from PIE root *men- (1) "to think"). The usual compound in Greek was amnestia, but this had a specialized sense of "forgetfulness of wrong" (see amnesty).
<a href="https://www.etymonline.com/word/hypermnesia">Etymology of hypermnesia by etymonline</a>
Harper, D. (n.d.). Etymology of hypermnesia. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/hypermnesia