Hi... The negative incident you referred to in the beginning is the trigger and may not be the cause.
Something was already there in your subconscious mind which got triggered by this incident and caused you to feel this way.
Ask yourself, what is something major that happened to you or changed in the recent past?
Is there anything you have been repressing lately.
A loss of any kind? A person, a relationship, a career/job/degree, death of a loved one, even a loss of perspective/ideology etc.
You need to identify and work upon the cause to overcome this condition.
Next Steps
Consult a Psychologist.
Interpersonal Guidance and Counselling using Psychoanalytic and Existentialist Approach is required.
Health Tips
Mr. Gunjan Maithil
Senior Psychologist
Cell: nine six seven one three zero three one three four
Website: https://gunjanmaithil.wixsite.com/therapy
App: http://wix.to/fECHB08?ref=cl