Same. And yeah, that's a pretty classical sign of ADHD. Though, that doesn't necessarily mean you have ADHD. I've gotten alot better as I've gotten older and about now the only real symptoms I still have are procrastination for stuff like this (for actually important stuff that are time -sensitive, for work and the like, I force myself to do them immediately) and I tap my leg alot.
Once I learned about 'Executive Function' a lot of things started to click. I even struggle at work. My new job gives me a lot of freedom. There's a lot of stuff I have to get done but I don't have any forced structure or oversight into how I do it. It's up to me when and how I do these tasks, and so long as they're accomplished in a timely fashion no one bugs me.
I've found that making lists (usually using Notion, which I only discovered because of the D&D world, mainly thanks to
@SlyFlourish) helps. I catch myself stuck in a rut of not making any progress, I can go to my list and try and check off the oldest item/s on it. This same method works for D&D prep, though not quite as well. I find myself sitting down to make my list (Find NPC stat blocks, find a map to use, make slides for encounters, etc.) and then losing steam before I've even started. I start with Notion, end up on Reddit, or here, or YouTube, and then the next thing I know I've spent all of the free time I had allocated for session prep just meandering around the internet not actually doing anything.
I feel like with work there's the extra drive provided by the ever looming threat of homelessness, and when it comes to hobbies like D&D that isn't there.
I think this is something that also kept me from running a game for such a long time. I used to think I had to do this mountain of prepwork, and it was so overwhelming I couldn't get myself to do it. So then I just never felt confident enough to run a game. Now that I've learned how to actually prep (Again, this is big thanks to Mike Shea. The Lazy DM 8 steps method really helped me narrow down the field to what is actually important, and give me a focused goal.) I still put it off until I get down to the wire but I can actually do.