That is what happens. Confined spaces that have little oxygen are extremely dangerous and have had quite a few deaths because of them. Those who are working in them literally just feel dizzy and confused, fall asleep and die from the lack of oxygen. There’s about 100 deaths per year in the U.S. Sometimes even rescuers die because they don’t know about it as well. They try to rescue, get confused and die. Hypoxia is a terrifying thing.