Bipolar disorder, specifically Bipolar II. Can get pretty strongly hypomanic, but fortunately it never broke through to full mania so I never had to be hospitalized. I self medicated for years with cocaine and alcohol.
I don't know if it fed into it, more like a ClusterF, a snake eating its own tail. Both had to be dealt with in order for me to be healthy. Ultimately the self-medicating makes things worse anyway, it's an extremely short sighted and short term solution. Plus there are obvious side effects to medicating hypomania with cocaine and depression with booze.
Again, I don't see why this had to become a judgement about justifying drinking and using. They are comorbid conditions. They are what they are, and they reinforce each other. Untreated mental illness can easily lead back to addictive behavior. Part of a big plan needs to be treating the mental health issues AFTER sobriety, as the substance influences the treatment of mental health issues.
Although it's possible to remain sober without treating underlying mental health conditions, I don't know why you'd want to. It's a terrible place to be.