Oh I am so sorry that you are feeling this bad, it is scary, can not imagine the anxiety you are having right now. Hope you did or are going to take advice and head to the hospital. In March I was quite a bit problems with breathing and my CO2 levels up having bronchitis and pneumonia with no other signs except shortness of breath. Once they got all the misc testing done and gave me some valium to relax me, they came up with something called a BiPAP that was very helpful. Because of the valium I do not recall the 1st time they used it with me, but was willing to try it on the 2nd go around to the ER visit, for they did not realize at the end of my 8 day stay, they had sent me home with COVID (caught while in the hospital) and I returned in just 15hrs of being released again having just breathing problems, no fever etc... The ER did what they called a BiPAP rescue and then used it for a couple more days off and on, more so while sleeping.
Not saying this is what they might be able to do for you, but they (Medical Staff) are there to help you with the knowledge of todays medicines and machines that can assist. I now have been at home for over a month, back with just my normal stage 4 issues that I had previously.
I so wish you the best and would love to know how you are doing.
Hugs to you! Keeping you in my thoughts and prayers