Right, here's an odd one. I don't think anyone had similar experiences, but it's worth a shot.
I had a first asthma attack in July last year and have been fine every since, doing a lot of rather hard sport and having a good time. These last two weeks I had a rather annoying cold that has moved down to my throat/lungs now. Three nights ago I woke up in the middle of the night and had slight difficulty breathing. Took my emergency meds, which didn't help too much, but I fell asleep again. Was slightly out of breath the following day. Next night same story, only worse. Got the nebulizer out which also didn't help too much. All of yesterday morning I felt out of breath. During the nights and yesterday I felt like someone stole some oxygen from the air and not as if my lung volume was restricted. I had a blood test yesterday morning as I'm fighting with some other issues and multiple mineral/vitamin-deficiencies. I'd stopped taking all supplements about a week ago for that blood test.
Yesterday at noon I took my vitamin B12 shot and iron pills again. And guess what: a while later I could breathe normally again. Yes, I know you need both for red blood cells, but surely it cannot be more than a coincidence. I don't think both can have such immediate effect on oxygen transport both when stopping and taking them again, right?
Note: I am very slightly asthmatic which I only notice when walking around too fast, but I guess that it's either due to the cold or from the more difficult breathing, but that is manageable with the emergency meds.