My Sister Is 68 Years Old And Has COPD She

My sister is 68 years old and has COPD she also has fibromyalgia, general anxiety disorder depression that is being treated. She has not felt well for about a year. Lately, she has experienced sudden nausea, light headedness and shortness of breath with clammy skin. She had a Nuclear Stress Test a week ago and it came back fine. No blockages. We are stumped as to what is causing this, it is happening more often than it did in the beginning. What could be causing this??