I concur it is hard to keep continuity while battling waves of inconsistent motivation. While we hardly have the same experience with the issue, I would like to share a few additional models with you. They are not any close to a solution, but might be helpful thinking about:
I found Brain Hacking a helpful tool.
What incentives can you setup to use your own "instincts" in your favor?
"Long tail" projects are a very good call. If the required endeavor for success is big and challenging, you are likely to get drawn back to it out proud, "just to prove yourself". It might help assuming it is your responsibility to get it done. The waves will keep coming regardless, but I found that even in the dark moments, you can still advance, if just a little, and sometimes you will be surprised by finding out a time of complete aversion was exactly what you needed to step back up. I can see you are self-conscious of those moments so maybe an "OK, I am depressed. What is the least I can do while in this state of mind?" is a good exercise.
I got involved into a project that might take many years to finish and I became obsessed with it in a way the great majority of my thoughts, regardless of how messy, fall into its reign. Many might tell you to shoot for Balance instead. That sounds nice, but as an ADHD myself, I am not afraid of saying singleminded dedication to a cause is not as bad as people might tell you.
One way I found to cope with it is to apply Gamification in my routine. Every finished mission is one step less towards the vision. Another strategy I use is to go the opposite way of the norm by removing all source of information instead of feeding on them. I really mean no books, no articles, no podcasts, no HN, no YouTube, Twitter, Instagram or Facebook, etc; you name it, anything that would likely bring you anxiety. In this state of mind your mission will be canalizing your thoughts into something you find useful. Repeat.
To finish, for what it comes to career as an Engineer/Artist, I would say that following a passion, even if inconsistently, will likely be a better lesson, both technically and creatively, than any job you could find in the system. I once got two very good job offers by basically saying "I am too adventurous. I won't ever fit your archaic corporative structure. Are you sure you want me in?". That said, nothing really beats the thrill of being a maker. Have you ever lurked into Systems Design?