Hypoglycemic or anxiety?

If the 2 hr GTT was normal I highly doubt that you are experiancing hypoglycemia. You could however be having a cardiac arrythmia, the most common one in young adults is called SVT and can easily cause the symptoms you describe. Next time that happens take your pulse for a full minute and try bearing down and see it is breaks you out of it. Typically with SVT the heart rate will be 160 BPM or greater.