I'm really worried about my dad. He's 62 and was in the hospital for COVID-19 with a CT severity score of 2125. He needed oxygen support for about 25 days and was on a lot of medications like steroids and anticoagulants. Now, he's been home for a month doing physiotherapy and breathing exercises, but mostly bed rest. His oxygen saturation is fine when he's resting, around 97-98, but it drops to 90-91 when he walks or does any little exercise. Plus, he still has a bit of a dry cough. Can you help me understand when we might see his oxygen levels stabilize and what more we can do?