You ran out of capacity for coping mechanisms. Psychiatrist Dr Stephen Humphries explains how late diagnosed ADHDers cope through life by being bright. https://www.youtube.com/watch?v=lSjHYiTEA4M

I got on by having modular work (university, software engineer with Jira tickets overseen by a PM) which is small enough to still be done last-minute, constant manufactured anxiety to get me to get things done, being excused for being young and foreign (for being rude). Shit Life Syndrome and maturity (expectation to be responsible) meant exacerbated ADHD symptoms and a diagnosis.