I've been there several times but I'm the last person who should be trying to give anyone else advice about how to deal with it. I have my own methods and coping strategies that just about work for me but I wouldn't recommend them to anyone else. I used to burn my own work all of the time because I thought that it was rubbish and that I was useless. Used to drive my agent nuts. Three failed suicide attempts but it turns out that I'm just really crap at trying to kill myself. It just never worked. I'm struggling a bit now but I have people who rely on me so I can't do anything silly.