We see only the good; those forgotten memories including a kaleidoscope of 'happy times' that we do actually miss, and have not been repeated again in our life. But, when we extend our recollections to include what went wrong, or was perhaps the reason for leaving a place, a job or a person behind during that life phase, we remember the pain and the suffering we experienced at that time, that perhaps the good moments were masking.
It can all come flooding back; our mind suddenly making us fully aware of memories and experiences we've not thought about since they happened. This can result in raw emotions suddenly surfacing. A difficult experience to relive, especially if those recollections were extremely traumatic. The mind losing its filter, as we've somehow actually time travelled, with our consciousness, back to those events. The mind confused, permitting its filter to be side stepped.
We are pure consciousness after all; our living thoughts and experiences being infinite; past, present and future being a concept of the human mind. So when we transcend the limitations and controls of the mind, we are able to re-visit any experience past or future. To re-live and re-experience. A concept that can be often related to deja vu ... when perhaps our pure consciousness has already seen an event ahead of time ... so when the event occurs, our consciousness trapped by mind limitations somehow remembers the event from somewhere.
The mind is not us, it is a field we use as a witness to the experiences we are. For we are living energy creating physical experiences in this realm of water and sound.