Anxiety is created by the immune response, breathing difficulties are from toxic build up and the body's inability to release those toxins. Many toxins are created by the infection. When the toxins build then anxiety is increased.
Vitamin C for me is the best antioxidant and using high doses is sometimes required. I would take with drug therapy since it may minimize the effectiveness of the drug. There are a number of herbal products that can reduce anxiety such as valerian, hops, passion flower etc. Those are usually sold as combinational products.