Hi...I too get those feelings..I have been experiencing gallbladder problems since march, my dr thinks its anxiety making me feel like that though...Like you, I can be sitting there doing nothing and all of a sudden I get lightheaded and nauseated, feeling like im going to hit the floor, my heart racing, scaring the heck out of me.....I went to the emergency room and had a cat scan done,had an ekg done too and they came back fine..So im guessing maybe it is just anxiety..Now when it happens I try to talk myself through it, staying calm, just repeating, your fine, your heart is fine, your head is fine....Seems to help...Good luck...:-)