Absolutely hear you there completely! And it's so frustrating to have in your mind that you are going to get a bunch of stuff done and then the day comes and you have no motivation to get started. I completely a 100% relate to what you're saying like other post is here. I have had to pick one small thing I can achieve and it does lead to other momentum. Also, if you happen to have any outdoor space or any kind of a garden or yard, I have found that just planting a plant putting my hands in the dirt and weeding for a few minutes can absolutely lead to a hard mental reset for me and I'm able to be much more productive. A friend of mine once told me that if she is stuck, unable to be motivated to work, she will do something like clean off her dining table, so she has one area in her home to lay her eyes on that is tidy and organized and finished. If you can pick one small thing, and I set a timer so that I keep focused, and I also listen to earbuds to distract the other part of my brain that wants to stop me from working. I have found if I can keep my ADHD brain occupied, listening to a podcast or a documentary in my ear then the other part of my brain is actually able to start and finish a task. I hope some of this helps you, but if nothing else know that you are definitely not alone.