If you dream about your future, you are only projecting your ambition. On the contrary, if you dream about the past, it is nostalgia. Though named dreams, both take place only when you are awake.
But there are two other kinds of dreams. If your dream defies logic, is extravagant and is a product of wildest imagination, it is fantasy.
Coming to the dream about the past, if it is of the type “If only I had…”, it belongs to the ‘sighing in agony’ or ‘brooding over misery’ category. (eg. If only I had chosen some other job…., If I had only married some other woman….)
Here, we are dealing with the ‘recalling the pleasant experiences of the past and a longing for the same’, though you know the past is past and you cannot hope to get it again.
Do I plunge into past memories ? I do. Quite often. I often think of my boyhood life when everything was fun. I left no tree un climbed, no irrigation tank unconquered, no well in the village, the depth of which was un fathomed. Of course, you have to be brave enough to receive the glorified tributes your parents shower on you when you ultimately go home when hungry and find that your heroic deeds have already reached the ears of your parents.