Some of the most recognizable signs of dissociation for the person experiencing it are a feeling of being disconnected from your body or surroundings.
Time may seem to pass very quickly or very slowly, and that person may be unable to experience the proper emotional reactions. They may feel as though they are watching themselves as if they're watching a movie.
To an outsider, dissociation may not always be easy to recognize. If a person seems like they're zoning out, not responding to stimuli, and have a blank expression, they may be dissociating. This is especially common after someone experiences trauma or has been diagnosed with a mental illness.