Familiarity is not usually a cause for concern as long as it is attained by objective memory. Objective memory is the memory in public space. If your memory follows a sequence from cognition to recognition then your memory can never throw you off guard. It is only when the process of becoming familiar and the state of being familiar(familiarity) materialize without time lapse that you call it an out of the ordinary experience.
You feel that no experience or sensory perception is new and whatever is happening has already happened; you can remember it as though ‘today’ was ‘yesterday’ meaning the present that is supposedly new belongs to the past. Novelty in quality is lost because the so called new experience is mapped to a similar experience in the past. Novelty in actuality is lost to similarity in quality. Misplaced similarity is familiarity.
You feel compelled to process every experience right from an abstract emotional transaction to obscure and common place sensations. At some point your mind, the reservoir of experiences, gets overwhelmed by the volume of what it has stored. So it is the memory of a sensation that is recollected and confused with the memory of the experience. The memory of a prick for example is confused with the memory of a pin. You have felt both before. Even if in reality you are experiencing a unique prick of a unique pin for the first time, the sensation is the same, painful and irritatingly shocking.
Supposing, the memory of experiences in the public space is a reservoir of events and in the process the reservoir also stores all reactions to the events in the same place then it is quite possible to confuse sensation with experience. The example of a pin is a common place one. Even in the case of more powerful instances of emotional impact the model is the same. It can also take a more abstract form, where, in public space you are learning a concept for the first time but you just get a strange feeling within that you have already learnt it before in exactly the same circumstances. It is possible to map concepts so quickly that you do not notice your participation in a cognitive pattern.
So this maybe about memory in the private space which in public space is declared impossible. But the common sense paradigm relies heavily on the sequence of outcomes. You cannot possibly call an experience new if you are absolutely sure that you have experienced it before. Your reaction may change if that be the case. You aren’t sure so that’s why you find it strange and incongruent with the so called reality.
The sensation of an experience is more or less the same for all experiences of a similar nature so it is highly possible to confuse sensation of an experience that you are about to surpass with the memory of habitual reactions to similar experiences in your past.
“I’ve had this prick before is too common place to receive importance” but “I have a strange feeling that I have met him before in the same place and same time and exactly under the same circumstances” is not. It is because of confusion in your consciousness that you mistake revolution for rotation.