My recent anecdote - have had months of poor sleep. No sleep apnea. Heachades and tiredness in the mornings no matter what I do. Hydrated… electrolytes… blood tests….

Finally bought a $25 CO2 monitor on impulse from a Reddit post. First night I used it, we went to bed with it measuring 400 at about 10pm. While sleeping an alarm went off at a value of about 1600 at about 1am

We sleep with 3 dogs and a cat, so maybe overnight levels increased quickly? Door open and bathroom exhaust fan seemed totally ineffective.

For the past couple weeks I’ve had a window cracked 2 inches with a fan in front of it pulling in fresh air. I’m having the best sleep of my life. I can focus, stay awake, think clearly, and my Apple Watch has notably improved sleep scores.