Leo, even when not sleeping, breathes very poorly.
Oxygen saturation drops far below 85%.

This means he needs constant oxygen backup. 

If the situation doesn’t improve, he will go back home with an oxygen concentrator.

An oxygen concentrator is huge, heavy and stationary.
It means no more walks, trips, laying in the sun, meetings with the doe,
or searching for boars. Leo will not be able to leave the apartment…