Stress test, echo, two week holter all normal. thyroid, other blood work all normal. having fluttering/skipping/racing heart beat of varying duration, severity, and timing. could this be stress/panic attacks or even a hormone imbalance?

Keep a diary on what brings them on. Dudu not have any during Holter? . Discuss your diary with your Dr.

The fact that all your tests have been negative for significant heart disease is significant and reassuring. If you had the same symptoms while on the Holter, I would say that your symptoms are are not due to a cardiac arrhythmia. I do not know what is meant by "hormone imbalance" but your symptoms could certainly be due to stress/panic. Please follow up with your doctor for continued observation.