Originally Posted by Rjinn

In terms of reactive depression experiences do cause it, but that's temporary and not a clinical disorder. Also just a normal reaction. Any chronic illness is caused by genetics, is biological or other illnesses. For example pot doesn't cause psychosis, it only triggers it as an onset. Psychosis is a pre-existing condition same as depression, bipolar disorder, and schizophrenia.

I'm sure you are talking about PTSD but that's also just another trigger for depression.