What are the differences between depression and ptsd?

Good question: In ptsd, the person experienced something traumatic and constantly relives it, tries to avoid things that remind him of it, & is always "on alert." this has to go on for at least a month. All of this causes distress or impairment in the person's life and/or relationships. In depression, the person is sad and/or irritable (to a greater extreme than is normal) and may not know why.

Dr Fowler agreed

PTSD VS depression: Ptsd is an anxiety disorder which often has depression on top of it. But ptsd is characterized by there having been a traumatic event which begins to pervade the persons life --- dreams, avoiding situations that remind them of the traumatic event, etc.

Dr Fowler and another doctor agreed

See below...: Depression is a mood disorder whereas ptsd is an anxiety disorder. The theme in depression is one of sadness; in ptsd, it's one of fear and nervousness. While a traumatic event may have happened in the life of a depressed person, the occurrence of a traumatic event is a requirement in the diagnosis of ptsd.

PTSD always involves: A traumatic experience and three types of symptoms -- re-experiencing the trauma, avoidance and emotional numbing, and excessive arousal (feeling nervous, stressed, jumpy, etc.). Depression is feeling down, pessimistic, unable to feel pleasure, loss of energy & interest in doing things, changes in sleep & appetite, difficulty concentrating, and being self-critical. You can have both at once.

The interplay: This question was well answered by a panel of md's. Where complex, severe ptsd is present, there is often an interplay with depression. The hypervigilence & autonomic arousal of ptsd can be constant. This eventually leads to burn out with no energy, no motivation, no social interactions & no hope. The individual moves back & forth between fight & flight to an exhausted, demoralized state.