Declarative memories, comprising explicit knowledge of facts and experiences, are known to be dependent on the hippocampus. This study posited the CA1 subfield of the hippocampus as a pivotal neural locus for retrieving past experiences. We hypothesized that if the behaviour associated with these memories is not congruent with the current sensory information, it creates an internal conflict, potentially leading to a mixed-reality perception that suppresses the solely sensory or memory-driven behaviours. Employing the tet-tag system and optogenetics in transgenic mice, we activated memory ensembles to assess behavioural responses in aversive versus neutral contexts. Our results demonstrate that reactivating memories of fear have no effect in the same context, indicating an absence of conflict. Conversely, in a neutral context, hippocampal activation disrupts standard behavioural patterns due to conflict with current sensory information. Notably, specific cortical regions detect these conflicts, and failure to do so leads to the emergence of fearful behaviours. These findings shed light on how the cognitive mechanics of memory recall and its interaction with sensory inputs shape the behaviour. Furthermore, the role of the cortex in identifying conflicts between memory and sensory inputs emphasizes its significant influence on behavioural modulation.