Most of the claims are trivially verified true with a proper understanding of hypoxia and the effects on the brain.

Of course you want to be sleepy, but you don't want that sleepiness to be due to hypoxia because hypoxia is known to damage the brain.

The link you gave makes me think I actually have to dig through quite a few studies to find something supporting what you said (it's not on the first page, for anyone wondering), which is why I asked for direct sources.

A simple search of "hypoxia from excess CO2" brought up https://en.wikipedia.org/wiki/Hypercapnia, which also support the claims.

Please, for the love of god, learn to google properly: http://www.catb.org/esr/faqs/smart-questions.html