The blood test prabably ruled out hyperthyroidism. Your symptoms can be heart related, and it may be a good idea to have any heart issues ruled out. A congenital mitral valve prolapse condition can cause your symptoms:
Lightheadedness, dizziness, or both can occur when first standing up. This feeling is usually associated with a sensation of a forceful heart beat or palpitations. These symptoms may be related to decreased intravascular volume and metabolic neuroendocrine abnormalities.
Shortness of Breath. This is usually described as the inability to take in a deep breath. It may occur at rest or with activity. The shortness of breath has not been found to be related to cardiac heart, or pulmonary lung abnormalities.
Anxiety and/or Panic Attacks, although the relationship is not clear, many MVPers suffer from anxiety or panic attacks. The symptoms described are more consistent with panic disorder, the anxiety disorder studied most often in MVP patients. People have recurrent, spontaneous anxiety attacks that consist of various combinations of symptoms similar to some MVPS symptoms. These symptoms include: fatigue, fainting, dizziness, chest pain, lightheadedness, rapid heartbeat, heart palpitations, and shortness of breath.
Mitral valve prolapse is a condition where the valve leaflets that normally close and prevent backflow of blood into the left atrium; MVP happens as result of elongated chords that attach to the leaflets to close the valve do not close the valve and leaflets bellow into the atrium as result of the elongation and left ventricle pressure during the pumping phase.
I agree with kenkeith have your heart checked out. I too suffered from panic attacks but now control them through breathing exercises and had hypnotherapy done. I used to go the hospital as I thought I was having a heart attack. I think the doctors got sick of seeing me there and put me on a puffer the ones that asthmatics use. Everytime I felt my chest tightening I would take a couple of puffs that eased my chest, then did my breathing exercises. (don't do it anymore, the puffer I mean) At that time I was desperate if you never had a panic attack you don't know what it's like. I feel for you, hope you find something to help you.
i had a friend that worked in a er in nyc she told me weekends were the worst ppl come into the ER with all kinds of illness they find nothing yet these people feel very sick panic attacks run different from one to another i had a ruptured disk took 6/mos to find that after that i got a ulcer in the dadoul whatever i got panic attacks tingling dizzy afraid to go out dizzy i had to grab the manhole put my fingers in the holes so i wont fall into the sky ran across the street the curb was 7ft high doctors did not find out what was wrong how can i go on this way three kids lousy home life ready to give up went to a family doctor who found my problem put me in front of of his old floscope wow butterflies spasms took a GI found a pea size ulcer took med it did not help went to a party sipped on ice cold water started to feel better went home filled a pitcher with ice and water sipping not drinking in a short time the panic attacks went away so did other things it took 10yrs to find what i had theres a lot of things that can bring it on there are ppl who will not travel underground i drove a nyc taxi who should know ppl like a cabbie i had all the systoms i know what u are going through all this happened when i was 30y/o i have HBP had a HA 9/05 check yourself u might cause your own problems so anyway if u are not happy with your life and cant get out u fear to be lonely i know what it is i done the whole 9yds seems that u are missing something that a doctor cant cure u know yourself then help yourself i am 77y/o trying to stay around longer good luck