I've mentioned this on HN before and got some good ideas in replies[0], but I still can't find a formula that can bring that state back. Unfortunately, I concluded that the most plausible answer is somewhat dysfunctional and... "base", for a lack of better term - those hyperfocus achievements had a big component of impressing my peer group. They started with me telling myself or someone else, "like hell I/we can't do X, hold my beer...". Something I can't really recreate these days.
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No problem, start Climbing and Mountaineering you will learn really fast that there is no low commitment, not a community or other peoples that can push or judge you, the situation (nature) demands that from you, there is no NO, and there is no give up. At the end of the day you feel like buddha and superman, repeat that 100s of times and your focus will compleetly shift away from the commitment standpoint to the "what do i really wanna achieve"-point the rest is nonsense and will come automatically.
It's interesting because I'm currently at that crossroads in my life. I just left the PE that bought my firm and am unemployed for the first time in 20 years. Wife is freaking because loss of income is detrimental to the house we're currently trying to buy and just scary to her.
Building great things from the ground up with great people is where my passion lies. I'm not really the guy to get a job with one foot out the door or do 2 things halfways - and I know ultimately living my time passionately will win out. I guess I'm just saying that I understand where you're at, from an inverted perspective.
It's an exhausting life at times but feels well lived.
For me this is more a mode of operation. My way to relex is to be productive in a different field (e.g. to relax from programming I'd do electronics, build a thing in Blender, etc.)
You can do one yourself on understandmyself.com