Hi Wanda,
Please be sure to ask this question of your doctor for a more detailed explanation.
I think an easy way to describe the sensation you are referring to is if you were to consider how the body responds to a stressor. Think of the term stress here in general terms, for example as a demanding situation on the body the same way that standing puts stress our muscles and bones. The internal state that our body feels can range from tension, anxiety or strain.
I am not sure if this is the type of information you are looking for, but try to think of fight or flight response to "stress" as descibed above. The heart rate increases as does blood pressure. Our breathing may become affected. Hormones are released in the blood. The liver releases sugar, our pupils dilate to allow more light in, our muscles tense, blood flow to the digestive system decreases while blood flow to the brain increases. These are some of the physiologic changes that our bodies go through to ensure that blood )pumped by the heart)is carried to the more important areas of the body when faced with a "stressor".
Hope this helps,
Casey
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The Panic Center Support Team