The Vyans were a civilization of Humans who suffered a horrifying cataclysm which they would later come to know as the Vorlix. The Destroyer of Worlds, Linea, arrived on Vyus, via the Stargate, and began studying ways to reduce, or reverse, her own aging process. Using two test subjects, she released the substance Dargol into their bodies. Unfortunately, the dargol spread into the entire population (including Linea), making the elderly revert to their twenties and thirties- while simultaneously completely losing their personal memories, although they retained any prior skills and knowledge of how to sustain themselves- and anyone previously younger to disappear entirely.
Eventually SG-1 arrived on the scene to investigate the situation, and discovered one of the locals, Ke'ra, to have previously been the dreaded Linea. With her aid in genetics and a forgotten understanding of the substance, the Vyan people were able to return their original memories, mourning their reverted dead, but able to live out their lives once more. Ke'ra (Linea) chose to succumb to the original organism, which allowed her to forget once more and leave the madwoman Linea behind forever. (SG1: "Past and Present")