In contradiction to conventional damage annealing, thermally annealed H-implanted Si exhibits an increase in damage or reverse annealing behavior, whose mechanism has remained elusive. In this work, we conclusively elucidate that the reverse annealing effect is due to the nucleation and growth of hydrogen-induced platelets. Platelets are responsible for an increase in the height and width of the channeling damage peak following increased isochronal anneals.