One other thing that I would like to add.  I don't believe anyone on either side of my family to have died of any heart related illness as far back as my great-grandparents.  My father has an irregular heartbeat, which I just recently discovered, but I do not believe that it is anything too serious.

Hi Tom and welcome to the forum. I've read your posting and you should be aware that your concerns are extremely common among persons with anxiety and panic disorder.

Above all else, the most fundamental misperception that you need to address is believing that benign heart palpitations arise from the heart and also that they constitute a symptom of an impending cardiac event or risk your your life. This is absolutely incorrect and it's the very reason that all of your past diagnostic tests, including any future tests, will always produce a negative result.

Benign palpitations such as those you are experiencing do not originate from within the heart at all and do not under any circumstances constitute any classic form of cardiac arrhythmia. It' merely inappropriate stimulation of the heart by the vagus nerve. You can think of the events being more related to a common muscle twitch that occurs elsewhere in the body. Remember that the heart is as much a muscle as it is an organ and as such , is vulnerable to such stimulation of this type as much as any other muscle in the body.

If you experience any type of GI difficulty such as indigestion, bloating, changes in bowel habits or similar disturbance, then realize that benign palpitations can be among the physical symptoms experienced. This is because the vagus nerve innervates the GI tract as the pneumogastric nerve. Disturbances at the level of the GI tract can cause a wayward evoked potential, or nerve impulse, to be generated that travels upward along the vagus nerve proper until it reaches the terminal endings of the vagus nerve, including the spleen, heart, lungs and larynx among other areas. Naturally, the dynamics of the heart muscle in action cause the most dramatic response that is dependent upon precisely when the signal reaches the heart during the cardiac cycle.

The lungs can also be affected and many patients describe the sensation as sometimes feeling that the lungs have forgotten how to breathe on their own and subsequently, voluntary control is induced. It is also common for the vagus nerve response to stimulate the musculature of the larynx, often producing the sensation that a foreign body is in the throat and possibly occluding the airway. Swallowing may seem uncoordinated. The combination of vagus stimulation of the lungs and larynx, together with any pressure that may be occurring against the diaphragm as a consequence of GI bloating, can convince the sufferer that they re experiencing shortness of breath. Consequently, constant efforts are induced to try and yawn or otherwise achieve what is known as an inspirational breath, or a breath that fully stretches the lungs and produces full tidal volume inspiration. An inspirational breath produces a mild calming effect and appears at random during the normal respiratory cycle.

Panic disorder is typically the result of disturbed sensory feedback that usually culminates into a panic threshold. The sufferer senses a rapidly growing sense of fear and forthcoming unidentifiable event. Realize that under normal circumstances, the body provides the brain with constant sensory feedback and it is the brain's response to the feedback which regulates physiological homeostasis by comparison to the environment.

The body's sensory functions can become dysregulated by the effects of anxiety and consequently, the brain is unable to correctly interpret the collective sensory data being received. The sufferer generally senses odd changes in physiology most often mistaken for symptoms that something is wrong and the subsequent fear rapidly accelerates the feedback and response to the extent that it feels as though something catastrophic is about to occur and yet can't be identified.

Rapid, shallow breathing also produces a mild blood gas imbalance which, together with sensory dysregulation, produces racing thoughts and confusion, all of which escalate to the point of a panic threshold event. Panic events can be set in motion by something as simple as a change in lighting, particularly artificial lighting such as florescent lights  can set the process in motion.

The basis for recurrence usually centers upon a growing lack of self-confidence and trust in one's self. The panic attacks produce an ever-present sense of vulnerability, with no way to predict when the debilitating events might occur. It is this perceived helplessness which can result in social withdrawal and a daily routine whose focus is upon proximity to safety, ie a hospital or emergency services.

The original onset of panic threshold can arise from even the most insignificant events. It is the interpretation of the event which causes the ultimate pattern of panic events to arise. Understand that the brain in all humans bears a function known as the fight or flight response, originally intended to prepare the body to either fend off a threat or alternatively escape from it. In order to do so, the brain induces a broad and rapid up-regulation in physiology such that the body is best prepared to survive. If you've ever heard someone who has just been suddenly frightened by a loud noise, they might exclaim "That made my heart skip a beat!" What these people are describing is the exact same palpitation event you are now experiencing, except in your case, anxiety and fear causes the fight or flight response to remain engaged in a chronic fashion.

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