This problem once sent me to the ER too! I was driving my kids to Kid's Day Out and got so short of breath I started to have tunnel vision. I went to the nurse's office at the big church where my kids went to KDO, and she had to call my husband. When I got to the ER, they couldn't find anything wrong with my lungs, heart, or oxygen saturation, so they decided it was an anxiety attack. Patted me on the head and sent me home with tranqs. I looked at my husband and said, "Did I seem anxious to you?" He said no, I seemed very calm. I've been afraid to mention it to docs ever since for fear of getting the same reaction.