Todd Wilson was a Jedi who suffered from depression because of his guilt.
Todd, I saw as primarily suicidal. Much of it was remorse. He did many things that made him feel bad.
—A psychologist on Todd Wilson's depression
Major depressive disorder, commonly referred to simply as depression, was a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem, loss of interest and/or pleasure in normally enjoyable activities and lack of energy. Depression could be caused by many things, including having a bad life, loss, abuse, and remorse; remorse being the most prominent feeling that lead to depression. Depression led to suicidal tendencies, though it only rarely led to murder.
At times depression was a symptom of Repressed Anger Syndrome. The depression caused a normally calm person to explode in violent fits of rage.
Depression created negative emotions which could drive a person to the dark side. Todd Wilson was diagnosed with depression. His guilt and anger at himself drove his depression, which led him to the dark side, eventually making him commit the Jedi Temple massacre. SBI and Jedi investigators were initially puzzled about his behavior. His journal read that of a boy on his way to suicide, not murder.
Camilla Sookanado, a Rodian and former bounty hunter, also suffered from depressive episodes, which stemmed from her post-traumatic stress disorder.
Cole Kroger, a Jedi Master and President of the Galactic Confederate Systems, suffered from depression while he lived in the Milky Way galaxy due to bullying from his school mates.
Firmus Piett (LadyVader) suffered from depression due to loss much of his life, he blamed himself for his father's death. The only time his mother ever slapped him in her life was when he told her, 'I should have died instead of him.'
I should have died instead of Dad. I should have been there to save his life, to help him and I wasn't.
—Firmus on Qui-Gon Jinn (LadyVader)