Sleep-associated hippocampal reactivations are thougt to be central to the processing of memories and in particular to their consolidation. Nevertheless, it is unclear whether reactivated assemblies are static or whether they reorganize gradually over prolonged sleep. In this study, we tracked the neural activity of principal hippocampal cells in CA1 from the acquisition of a spatial memory, through an extended rest period (~20 hours) to its recall. We applied multiple decoding strategies to track the evolution of memory related activity over several hours of sleep.We observed that while during this period neural activity underwent a progressive reorganization, shifting away from the initially encoded configurations and started to resemble those seen in the subsequent recall session, this phenomenon showed a strong dependency on sleep stages. Periods of rapid eye movement (REM) sleep and non-REM (NREM) had antagonistic roles: while NREM accelerated the assembly drift, REM countered it. Moreover, we identified a persistent subset of cells that maintained unaltered reactivation patterns and linked the acquisition and recall of the memory, coexisting with a plastic subset which either left or joined the memory representation over the course of sleep and which mainly contributed to the observed drift.