I do get the blockage, sometimes both nostrils. As soon as I take magnesium first my sinuses unblock then the SOB diminishes substantially. I also get the uncomfortable feeling of the breath getting stuck. I'm fairly sure my issues were related to nutrient deficiencies. The body relies on certain substances to perform it's functions. If it doesn't have them, havoc ensues. For example, the mineral potassium is responsible for the contraction and expansion of the lungs (see my previous post. I do not recommend supplementing potassium unless under a doctor's care as the pills can be dangerous. But there are plenty of potassium rich foods available to us on a daily basis that we can consume with no side effects). Magnesium and potassium are closely related. If one is deficient in one, they will have issues with the other. Magnesium is also responsible for controlling both allergic and inflammatory responses. My theory is that once my magnesium dropped, the potassium did as well which set off a string of responses including poor lung expansion and contraction. Some people have said it works in reverse: you can't absorb magnesium if potassium levels are low. Once the magnesium drops the sinuses are either inflamed or over-reacting to every day substances in the air (allergies). I don't have an exact theory and didn't need one. Just wanted to feel better and by going the nutritional route I do. I can have longer stretches without a case of SOB and when it does happen, it's very manageable. Initially, I had to lurch forward or double over to breathe. One day when it first began I was driving. I almost wrecked my car.

Here are some other things I found during my search for a cure that might help someone:
In regards to c02 and overbreathing. Holding breath for a period will help balance that, so will bag breathing. For me it was a temporary fix and can also mess with your acid/base balance. If you're desperate you can try it but I wanted to get to the root cause. Slow to moderate exercise will correct c02 balances with time. I walk daily. It's recommended that you not over exercise as this causes your body to skew in favor of oxygen. If your overbreathing is related to anxiety. Magnesium will help that.

For those with trouble breathing in humidity. I had that years ago and it was completely eliminated once my magnesium levels were balanced. What felt like spasming vocal chords as well. Anxiety, gerd all gone too.

Some may have SOB due to b12 deficiencies. B12 has an effect on oxygen. Not a doctor but if it resonates with whoever is reading this post, you might want to check into that.

Vitamin C - find a vitamin that uses the buffered version or all natural form as ascorbic acid contributes to acidity in the body and that can throw your body off balance.

For some SOB could be an issue related to acid/ base balances in the body. This level needs to be tightly controlled. Do your research.

Everyone is different. You have to find what works for you. For me nutritional balancing is the route I took and I now see light at the end of the tunnel. I hardly notice it when it does happen. A good quality multivitamin that has balanced nutrients and a good diet that includes greens, fruits and greens powders, low sugar and potassium rich foods has been extremely beneficial for me. Sleep is important as well as water. Dehydration causes an electrolyte imbalance. A healthy lifestyle has been my weapon of choice. Do your research and find the will to make lifestyle changes. Hasn't been super easy but it has worked. See my previous post for more details. Hope this helps someone.

Lastly, if you're in the middle of an attack of SOB, calm down, sit and lean forward. You might need to stretch your body slightly upward. It will provide some relief.