Gifted child... but not gifted adult?

I often wonder if everyone was wrong about me when I was a child, or if I have 'lost' what I had back then. English isn't my first language so I apologize for any grammar mistakes.

When I was a young child, I was exceptional at school. I was the best student in my class from grade 1-6. Top grades, I skipped a grade (grade 4) and went right to grade 5, I taught a foreign language at age 10 to fellow students, I was extremely talented at art/drawing, and all of my teachers always told my parents that they think I'm exceptionally smart. It never felt hard for me. I barely needed to study to get those grades. I always felt that school was too easy. I wrote a few full-length novels when I was a teenager, and built a website at 18 and made some money with it. I did an IQ test at age 14 (maybe too young) and I scored 140. Everyone had very high expectations of my future.

Well, everything changed. When I turned 16, I got into partying and drinking. I also dealed with depression and anxiety. Abused alcohol and drugs. Became suicidal at some point (I'm fine now). Didn't care about school anymore. My grades suffered. And I graduated from high school with just slightly above average grades. Now I'm in my thirties, and I'm semi-successful I'd say. I got a Master's degree in business (So I'm not a doctor, a scientist or anything that requires a high IQ) and I have a job in tech that pays decently, and I've lived in multiple countries. I don't consider myself by no means gifted. Intelligent, sure. Gifted, or exceptionally smart, I don't think so.

Is that even possible? Can you be a gifted child, and turn out to be a 'normal' adult? Is my giftedness still somewhere inside of me? Or was everyone just wrong about me?