What a bunch of whimsical BS!

1) "thời gian phổi tự thải độc là khoảng 3-5 giờ sáng'

Seriously? Your lungs and body doesn't wait that long to exhale noxious or harmful fumes, irritants and or foreign substances. It will try to get rid of it immediately.

2) "Chú ý sẽ nhận thấy chúng ta hay ho vài tiếng vào khoảng thời gian này"

There are way to many other factors at played but just focused on one factor. You have been sleeping for 4-6+ Hrs. long in the supine, prone or any other positions in between. Gravity is at work and just the normal lung surfactant, water, irritants, junks and etc ... will have a tendency to aggregate in certain areas more than others. When the concentration is high enough, it will automatically triggered a coughing response.

3) Unless sick and or have some sort of illness, inhale & exhale normally. If you want to get to that very tiny last 5% of your lung tidal volume, give a deep, big and long yawn.

Very simple .. follow KISS