Coupled with the trigger of feelings is the fact that those feelings are often associated with loss. By the time you get to recovery, you have had multiple losses in your life, often related to childhood, many times due to being raised with abuse, addiction, mental illness, etc. While you may have experienced trauma within your original family, pain of loss may be from a specific situation.
You may have experienced the loss of relationship with your parents or children, the death of friends, or family; abortions, or career or work opportunities missed.
As an addict, you are likely to have experienced losses related to health issues. Perhaps you have Hepatitis C, HIV, or injuries due to accidents. It is not that you are suddenly thinking about these losses, but there may be a physical trigger. Perhaps you are in treatment and you see other people's children come to visit, and you have three kids and you don't even know where they live. Your daughter tells you that your ex-husband has just moved in with someone else. The goal is not to dwell on your losses, to not live in the pain and anguish. This is what happens when you don't acknowledge them and what they mean, triggering you back to your using behavior. With some loss you can only grieve and ultimately come to find some meaning from your experience; with others, in time, you can attempt to repair damaged relationships.