Hey Emma,
Congratulations on your promotion. Also congratulations and realizing you were understimulated and did something about it. It's important to know yourself especially when you have ADD. Change is always scary especially when you bet on yourself. But it's always worth it in the end even when it doesn't work out. Regrets about missed opportunities hurt more then past failures.
The first few weeks (months?) may be difficult. But that's expected and I do recommend working harder or longer for that time period anyhow to get a good first impression of yourself. After that you can scale back to a sustainable level for yourself. You got this!!!!