There are ways in which you can make that distinction objective to a certain degree. For example, by looking at responses that could be generated in the brain to exactly the same stimulus and there could be differences there.
Antonio DamasioThere is a sequence of events in our lives and so there's a temporal aspect to our experience that brings by itself, sense into the story. In other words, you were not walking before you were born and you were not doing X and Y before you did something else first. So there's a sequencing of events that imposes a certain structure to the story.
Antonio DamasioWe can be more or less conscious when you create grades of focus on a subject that is flowing in our stream of consciousness.
Antonio DamasioWhat happens [in a coma] is that you lose the grounding of the self, you no longer have access to any feeling of your own existence.
Antonio Damasio