"If I don't want to wash a fence, I can't think about how to wash the fence. I go into complete lockup. I ask the question, "how do I wash the fence?" and the answer will not come to me.

I can't get to "first I need a bucket and water." "

This is so true! I'm ADHD, diagnosed and tried medications for a while, they helped, but had other issues so I stopped. What really helped was the realization that there are tasks where I can't even begin. I then gradually trained myself to think about the first thing and just focus on that. Don't feel like getting up from bed? Thing about moving my hand, then make it move the covers off, then move my legs and so on. Soon the momentum develops and I find it easier to do whatever I didn't feel like doing. Now my default is to just think about the very first thing and take it from there. It took me a while but has worked wonders for me.