Memories

What exactly happens to the mind when someone is struck by memories past?
Memories that hardly ever come to the mind, that they're completely forgotten and considered as never happened, are suddenly recalled into the mind and the conscious brain is unable to do anything except to fall into a trance. Not do I only feel the crushing feeling of missing something, but also I start to think about what I used to think at that period of my life. What my personality was like, what inspired me and what motivated me. I remember many of things that are related to the song, the image, the voice, the idea that provoked my memory of the past.
I've been struggling with memories and dreams for a long while. I just want to understand what goes on inside my mind. Another factor that fuels my interest in taking this endeavor seriously and studying the human brain and mind. The advanced degree of the sophistication of our brain that is even exceeded by the sophistication of the mind completely fascinates me. In addition to fulfilling curiosity, a more complete understanding of this issue would help me deal with it better.