"At all cruising jet altitudes, the PP0 2 is below that required to support brain consciousness. All jet wheel-well stowaways at these cruise altitudes will lose consciousness from hypoxia."

So they always pass out but sometimes are able to wake up and manage to get out. Barely. Usually they die.

Wish we didn't have places so terrible to live that a person resorts to this.

Wheel wells are heated from equipment inside, some measurements say ~ +20° C vs exterior.

Could the air pressure be higher?

When planes get holes does the inside pressure equal the outside.