The symptoms of a panic attack may cause the person to feel that their body is failing. The symptoms can be understood as follows. First, there is frequently the sudden onset of fear with little provoking stimulus. This leads to a release of adrenaline (epinephrine) which brings about the fight-or-flight response when the body prepares for strenuous physical activity. This leads to an increased heart rate (tachycardia), rapid breathing (hyperventilation) which may be perceived as shortness of breath (dyspnea), and sweating. Because strenuous activity rarely ensues, the hyperventilation leads to a drop in carbon dioxide levels in the lungs and then in the blood. This leads to shifts in blood pH (respiratory alkalosis or hypocapnia), causing compensatory metabolic acidosis activating chemosensing mechanisms which translate this pH shift into autonomic and respiratory responses. The person him/herself may overlook the hyperventilation, having become preoccupied with the associated somatic symptoms.
Panic disorder involves repeated episodes of sudden feelings of intense anxiety and fear or terror that reach a peak within minutes (panic attacks). You may have feelings of impending doom, shortness of breath, chest pain, or a rapid, fluttering or pounding heart (heart palpitations). These panic attacks may lead to worrying about them happening again or avoiding situations in which they've occurred.
The buildup phase of a panic attack is the most important phase, because it is when you can prevent it. If you are under chronic stress, you become worn down and have no reserve left. Anything can push you over the edge. But if you regularly reduce your stress through a combination of cognitive behavioral therapy and mind-body relaxation, you will have enough reserve left to handle life’s surprises.
So I can tell you that panic attacks aren't dangerous, but I recognize that this is "easy for me to say". If you're having anxiety attacks, especially if they're a relatively new occurrence for you, you might not be able to believe this right now. That's entirely understandable when you feel that your life is threatened! You don't need to take anything here on faith. Instead, check it all out. Test everything I say against your own experience, as you work your way through this site.