As we live our lives, any moments are registered in our minds, some are hidden away in our subconscious as they don't need to be remembered or our brains don't really want to remember them anyway. A message from your unconscious means that something is 'leaking' out which your brain is ready to remedy or go over. This unconscious can be days old, weeks old or even years old.
Quite often old ones are things we'd rather forget, new ones are those we tally with others to get a good picture. HTH