By the way, I forgot to add that I've been to all sorts of consultation. I've visited study psychologist, "just simply" psychologist, psychoterapeutist and also psychiatrist.
The psychiatrist said that my main issue is low self-esteem. She didn't give me really "real" diagnoses or mental illnesses, it seems. But I do suspect to myself PTSD. Although I am not professional. I just sincerely doubt that mere low self-esteem can create such dramatic reaction to writing of master's thesis.