Nostalgia or Depression

Nostalgia is a strange phenomenon, it makes even the bad patches of our lives seem good. It takes away the gravity from our memories. But what gives our memories this gravity are our reaction to the events of the past. It is our reaction to those events/memories that make those memories (further) negative and eventually give rise to depression. Obviously, we can not associate happiness with a sad event but we can minimise this sadness by reacting differently - by shifting our focus and/or perspective.

Further down the road when we finally disassociate the negativity with those events/memories we free ourselves from depression and if we are generally optimistic those memories may now induce a feeling of nostalgia. Optimism makes nostalgia possible. The events of the past are absolutely constant, what is changing (over time) is our perspective. Therefore, depression could be controlled and, in some circumstances, could be replced by nostalgia. All you have to do is shift your focus from the negative to the positive aspects and accept the past because it can never be changed. The sooner you do it the better.