I (M29) am considering reaching out to a girl (F26) I dated years ago

About 6 years ago I dated girl for about a month before she put an end to things. I know 1 month is basically nothing for most people but I really liked her and was very sad about it. I couldn't perform in the bedroom during our short time dating, and even though things fell apart for another reason, it left me with a feeling of embarrassment and sadness that lingers to this day. I realized afterwards that my issues were caused by ADHD and chronic stress which made me unable to get proper sleep and messed with my sex drive, and that taking sleep meds fixed my issues. I don't expect this to change anything at all, but I am tempted to let her know what was going on just to get a sense of closure and hopefully move on. Could I explain this to her over a message after having had no contact since, or would that be a crazy thing to do?