My lung function dropped from mid-40s to around 30 a couple years ago. It was a scary and difficult time in my life. I was already undergoing treatment for mycobacterium abscessus, which was ultimately the cause of my steep decline. My hospital stay ended up lasting 6 weeks, and it took me a couple months afterwards to get back to where I had been.
I understand how frustrating a sharp decline can be. When our lung functions drops gradually, we get used to it. When it falls all at once, it feels so hard to breathe.
I would encourage you to try to go out and walk as much as possible. It sounds like you were able to do that earlier this week, so hopefully that continues. When I had my long stay, I didn't want to get out of bed, but I did lose a lot in terms of strength and stamina. Also, try to do things that occupy your time: read, watch movies/TV, etc. and sleep as much as your body needs. I know it's hard not to worry, but try not to. For the first part of my stay, they weren't sure what was causing my health problems and that did make it more stressful.
Culturing the various myco bugs does take quite a bit of time, but they may be able to find the right drug cocktail in the meantime to get you feeling better. I hope things improve for you soon -- I'll be thinking of you. It's a difficult road, but one worth fighting. Good luck!