You mention irregular sleep as a factor here, did you ever try taking a nap every day to see if that helps?
The only time I've had this sort of hyper-productivity feeling, I was working out consistently in the mornings, and always napping around noon, maybe thereby giving a boost in energy levels for "the next stretch" of the day.
I also wish I could reproduce this sensation. For me, I think having clear overarching long term goals, that every routine action built towards helped a lot. Summoning the energy to get started is a lot easier if I have an obvious reason for doing it, and once I get started I usually felt great about it anyways.
I spent a few weeks trying to do short (10-20 minute) afternoon naps and they did work great for helping me transition from "day job" focus to "work on personal projects" focus.
In my experience, a good nap could take me from 50% back to 90% but other times I'd wake up feeling queasy, dizzy, grumpy or low-mood. I stopped due to those unexpected side effects, but it seems worth trying again in the future.
Working out consistently may be an important part of the picture. One thing I've learned for certain about myself is that hard workouts will destroy my energy level for the next 1-2 days. So no heavy-weight lifting, 3-hour bouldering sessions or long heavy-breathing runs. Adding in light jogging every evening didn't make much of a difference in either direction.
I may try something like a 2-3 mile run each morning and see if the morning exercise makes a difference.
The only time I've had this sort of hyper-productivity feeling, I was working out consistently in the mornings, and always napping around noon, maybe thereby giving a boost in energy levels for "the next stretch" of the day.
I also wish I could reproduce this sensation. For me, I think having clear overarching long term goals, that every routine action built towards helped a lot. Summoning the energy to get started is a lot easier if I have an obvious reason for doing it, and once I get started I usually felt great about it anyways.