Not yet, but after a really deep dive into it I’m 100% certain that the cause of what I’M experiencing stems from this. When your breathing is slower than 12/min you build up excess CO2 in your blood. It is called hypercapnia and if it is not severe then it causes drowsiness, daytime fatigue, and shortness of breath. If it is severe then it can cause lightheadedness, dizziness, headaches, and fatigue. If you’ve never checked it out you should!

Here is a good explanation. Note that your O2 saturation can still be at a good level when your CO2 level is too high!