I recently came across this by accident and your explanation jives.
I noticed I would get fairly fatigued, and have to take a nap around 11am every morning, and eventually found that it was basically every 4-5 hours, even mid-day too. I would take a 10-20m power nap and usually wake up feeling really good, I would even hit REM in that time.
Then a few months ago, I noticed when I was having this feeling I was usually ruminating about something, and it was something like grappling or repressed anger, AND what this did was cause very shallow breathing and "breath holding" patterns. And I've been doing a lot of work around Gabor Mate, MD's work lately and processing trauma responses so I was able to identify this and feel the feelings in a more present way, and in doing so, start very intentional deep, slow breath and exhales.
Compared to my shallow breathing and holding, my breaths became like 3-4x longer. And... to my surprise, the fatigue would pass in about 5minutes or so and I would not need a nap, and get my brain back to an "alert" state, as opposed to that "foggy" state.
I have been doing this for months now, and it keeps working. And now, this was really blurry because sometimes I would be genuinely tired from sleep debt from pulling a late night, and it was a similar feeling. So when I get a solid nights sleep for multiple nights in a row, then the breathing works to keep me alert, and helps me get more in touch with my emotions and subconscious thoughts rise up and become concious. I can detect the shallow breathing/breath holding fairly well now, but not always, and it is still a work in progress to make these breaths the default. The breathing does help me move through life much better now, and I walk slower, and not so rushed, and am more at peace with doing things in the present.
This actually wouldn't really be possible though if it weren't for a discovery that I breathed through my mouth my whole life (40 years) recently too. I learned about the "nasal cycle" and in combination with a deviated septum I have, my nose would plug up every now and then with no rhyme or reason, I thought it was diet for a long time but eventually learned about the "nasal cycle" where the turbinates in our noses swap the swelling to change the airflow every 4-6 hours or so. And when it swapped to my non-blocked septum side, my airflow would stop and I would be forced to breathe through my mouth. What this meant is that I could never develop a habit of nasal breathing my entire life. I started using Afrin about 5 months ago, and then stopped because it says not to use it continuously and you get a rebound when you stop using it. But then I found a Ear Nose Throat doctor/surgeon and presented my hypothesis to him and he confirmed that the nasal cycle + deviated septum hypothesis was correct! And he suggested I use Afrin plus a nasal steroid (Sensimist) together and that will reduce the rebound effect and that enabled me to use Afrin long term to stop the natural swelling of the turbinates in my nose. And, so I've been using Afrin for 3 months now and can breath so good through my nose now, and it is so sweet, and so precious, I can't imagine going back to mouth breathing ever again. I do have increased sensitivity to cold with the Afrin and my nose drips like a faucet. Or maybe that was because I never breathed through my nose in the cold to begin with? Regardless, I need to bring tissues with me in cold weather wherever I go.
And that leads to the fact that now when I noticed the breathing pausing, I can take big deep breaths through my nose and it feels so good, and calming, I can break out of the trauma/anxiety cycle and self-regulate with breathing.
I think the breathing cycle issue is mostly a trauma response from a young age and then it turns into a learned habit. This is the result of a caretaker not being there for me/us to help us self-regulate at a young age. The Wisdom of Trauma film and In the Realm of the Hungry Ghosts book by Gabor Mate, MD. really was trans-formative in my understanding of all this and success here, combined with other things as I mentioned above.
Sleep debt is also super duper real, and from what I learned in The Promise of Sleep by William Dement, MD. is that if I miss 2 hours of sleep one night, it can take 4 nights to actually catch up on that, like 30 minutes extra a night. I can't pay it back in 1 night, and that I still need to take naps. If we don't have sleep we will be in a chronic stress state forever.
I also was recently diagnosed with sleep apnea, after going to the doctor for fatigue and mentioning how frequent and predictable my naps were, I thought I had narcolepsy. They had to do a sleep apnea test first for insurance reasons before narcolepsy testing could be approved. This was when I was still mouth breathing, and I was waking up like 10 times a night from chronic back pain, trying to find that perfect position, so never really slept more than an hour without waking. I was fatigued. So Sleep Apnea came back positive and one of the explanations for the waking up, (had to pee a lot too), was that when the airway closes the body releases adrenaline to wake up or do something with the airway, the adrenaline increases urine production, and so I was also waking up because of having to pee, not enough air, or back pain.
I finally got rid of all the back and neck pain (of 20 years) using Pain Reprocessing Therapy (Gordon) and Compassion-based trauma therapy (Compassionate Inquiry (Mate) + Internal Family Systems (Schwartz) and started sleeping through the night, without CPAP, and then I tried CPAP for a month and was still tired and fatigued during the day. So I stopped using CPAP and only later realized that I may have been getting enough oxygen at night but wasn't during the day.
This is all one giant hurried mess of a story, but I wasn't going to post anything and figured "perfect is the enemy of good" and that this could help some people connect some dots in their lives so I just blotted it all out here.