Why do I have flashback episodes?

I was diagnosed with dysthymia 10 months ago. 1-2 years before my diagnosis I used to be acutely depressed. No bouts of crying or anything. I was just numb. I couldn't feel anything. Then I joined college and started living with my friend of 4 years. She had some undiagnosed mental health issues of her own, and she started showing extreme reactions for small things. Maybe she couldn't handle the big change of starting college and moving to a new place. Anyway, it started slow and kept increasing. She'd get upset, angry, she'd cry, scream at me etc. A lot of things with other people happened in between. She had a problem with my new boyfriend. I was always terrified during these episodes, maybe because I grew up with an unstable mother who used to have extreme reactions and outbursts all the time. I couldn't defend myself. I'd just cry. I started having panic attacks. I broke up with my boyfriend. 8 months into college I was losing my mind and started self harming. I was able to stop that pretty soon, but not my tears. I'd cry at least 3 times a day, but hide it. During summer break I finally went to a psychiatrist. I spoke about my 3 year long depression and got a diagnosis. What I didn't talk about was my episodes of flashback to all the incidents of last year that'd trigger my crying spells. My depression is better now, but I still have, maybe 2-3 times a week, these flashback crying episodes that come on suddenly, without notice. Help?