What Causes Difficulty In Breathing Along With Light Headedness?

I am female, 69, I have had symptoms of difficulty breathing and light-headedness for no apparent reason. I ve had it often over the years and it causes extreme anxiety. It seems to strike out of the blue and makes me very uncomfortable. In March 2013 I had my gallbladder removed. Tests were done, such as Cat Scans of much of my body trying to determine that I had a gallbladder attack. In all, the doctors were very happy with my physical and said I was in great shape. Last Fall, I had an episode of near-faint where I was rushed to the hospital and tests were done, such as echocardiagram and a whole gamut of other tests. All came out impressive according to the doctors. But I still have this symptom which scares me and no one can tell me why I have this. I am a poor eater, mainly because I have allergies to so many things such as all fish and shellfish, vegetables (!), flour, soy, rice, I CAN eat chicken, pork, and fruit. I ve lost interest in eating, but I do eat. I thought my symptoms of the breathing difficulty and light headedness might be from low blood sugar, but whenever tested, it comes back normal. I think mostly because I m not feeling that way at the time. I m just so tired of feeling this way with no resolution. It scares me to the point where I m afraid to go anywhere because I might faint. I HAVE done that and hit my head. My doctor can t figure it out and seems to think it s not a big deal...but it is to me because it s affecting my life. Thank you for any information you can share.