I had a bone infection as a child that took several years to positively diagnose (it ended up being osteomyelitis). In an attempt to help my body fight off the infection, I was prescribed a couple hours a day in a HBO chamber.

HBO can be prescribed for infections of various kinds that are otherwise hard for the body to eliminate without assistance or straight antibiotics. This study aside, breathing pure oxygen for extended periods does wonders for the body's ability to repair itself.

The upside of that time was that bruises and mosquito bites healed practically instantaneously.

Diving accidents