I'm not a doctor either, and I don't know if this helps or not, but you are not alone here. I do this exact thing. I can cut people off without a second thought when I am down and they say or do the wrong thing. It is definitely an attribute of atypical depression ("having a more intense reaction or increased sensitivity to rejection, resulting in problems with social and work relationships" from webmd.com), and from the reading I am doing I'm learning that it's also part of bipolar II. Then I find when I am back up again I am super clingy and want to talk to them all the time. I think it has to be related partly to the bipolar, but I have also wondered if it could be a personality thing. I've talked to my therapist about this a lot. She thinks it has to do with how I was treated as a child and/or just a coping mechanism to keep people from getting too close. Of course, when we talked about it I didn't have the bipolar diagnosis, just depressive, so it's still a work in progress for me.