I also find productive and unproductive days are cyclical. For me, it is very much a case of accepting myself. The years and years of critical messages about being ”lazy” are hard to overcome, but it can be done.
Remember that, for many people, the ”H” part of ADHD is just as important. It’s not just underactive executive functions we have to cope with, but also overactive motor functions. Find a way to be physically active on your off days. It makes all the difference for me. I find proprioceptive activities to be most helpful.