I used to drink an energy drink before bed and people thought I was super weird for it! I didn’t find out it was an ADHD thing until my therapist asked, I guess knowingly, how caffeine affected me and I went on this whole rant about it.
That is also because you regularly consumed caffeine, no?
If you took a 6 month long tolerance break, I would be interested to see if you still had that effect. Insomnia is not that uncommon of a symptom of stimulant withdrawal.