What Does On And Off Dizziness And Racing Heart Suggest?

On two occasions, after not eating for a while, (one time after eating Chinese food and this morning I drink green drink (kale and spinach, with juice) but delayed my breakfast.) I felt dizzy and my heart was racing. I went to the doctor (which is next door to my job) and he told me my blood work was ok, except my cholesterol was 226. My thyroid, my sugar, my iron etc. was ok. I suffer with a lot of gas. What could this problem be. I did my EKG, stress test, etc. last week. I take vitamins at present.