We have all seen flashbacks in movies being portrayed as a visual memory of a past event triggered by a current experience. In films, flashbacks need to be visual but the underlying aim is to express the emotions surrounding a past event. Flashbacks though are not necessarily visual or even on the conscious level but rather can be a feeling or sensation that appears to come from nowhere, triggering an emotional reaction.

People who suffer from depression are often victims of such flashbacks. If we are not conscious of these triggers from the past, we may end up acting in quite an inappropriate and even destructive manner.

Take a person who felt rejected by a parent in childhood. As an adult a certain tone of voice similar to that parent's voice may cause an emotional flashback bringing up memories of feeling like a burden, unwanted and powerless. The tone of voice in this case has a similar effect as the loud noise that brings up flashbacks of violence for a veteran of war. This memory and the feelings it brings up, of feeling unworthy and powerless, can be a contributing cause of depression.

People who are depressed often describe it as feeling like they falling into a hole or a dark cloud. This 'hole or cloud' can be a type of flashback of a very painful 'emotional' memory, often a type of trauma. Understanding that it is an emotional flashback can help people to understand and gain a sense of control over these very strong emotions that appear to come from nowhere.  

We all have flashbacks, probably much more frequently than we realize, and most of the time they are pleasant memories. It is only when they interfere with life that we need to bring them up and verbalize them, and recognize that they are not part of us but belong to our past. This is difficult to do alone and may require the help of a therapist. It is important to remember that depression is a complex illness with many different possible causes both emotional and physical. Varied treatment plans need to be assessed by a professional.