"Hello, I have a disability. I would prefer to do small pulls if that's okay."
If I join an instance and see the tank saying this at the start, I will go out of my way to be friendly and helpful to you and make sure you have a good experience, whether I'm dps or healer. Even small pulls can be okay, because generally your dps will burn through those small pulls quickly, especially if they're not casters.
Offer it as an option, and most people will be completely fine with doing it your way. You don't have to tell them you have ADHD, you don't have to disclose any personal history, but give a little bit and others are willing to help you out too.
If someone is so annoyed by small pulls that they feel they have to leave, that's their option too.