not causing chaos in his order were almost my dad's exact words

This strikes me as significant. You have ADHD, have you considered that one of, or both your parents do too? Were I to launch into unsupported speculation, I might suggest that your dad's fixation on order is how he's managed his ADD symptoms through a lifetime of being forgetful. By developing a habit of always putting the drill back in exactly the same place, he knows where to find it when he needs it. If it's not there, he might spend five hours looking, give up, buy a new one, and then find the lost one on the other side of the workbench where he forgot that he left it.

These habits, routines, mental lists of automatic actions that are really great for helping to make sure everything gets done. They're also really easy to disrupt if something doesn't happen the right way. If he's got a routine where he gets in the car, goes to the store, and buys milk, for instance, might be disrupted by the car being parked in the wrong place. If the car isn't in exactly the right spot, then the visual cues are different. Now he can't remember whether he's going to the grocery store, or to the doctor, or whatever, and has to stop and think about it. This adds a little stress. Being under stress makes it all the more likely that the next step in the routine gets disrupted, and the next thing he knows he's driven 15 miles out of town having totally forgotten why he got in the car in the first place. Don't tell me you haven't done something like that before.

So, he's built a world of predictable habits and routines that make his ADD symptoms manageable, and here you are threatening to bring back the dark times of forgetting everything. He's going to be frustrated about having to remember things again. He's going to be disappointed that you're so much like he was when he was younger (my dad tells me all the time "Why did you have to be so much like me?"), having to face the same demons, and knowing that you have to fight those battles on your own. And he's going to be offended that you're dealing with your symptoms in a different way than he learned to deal with his, that his method (and thus he himself) is wrong, and invalid.

Anyway, that's enough totally baseless speculation out of me. I won't be offended when/if you tell me I'm completely wrong and should just go away. On the off chance there is something there, it might be good to have a deep heart to heart with your parents. Or not. I'm really projecting my own experiences here, so feel free to ignore me.