Vasovagal episode: This response is similar to what may happen when someone stands up too quickly from a seated or lying position, has been standing in one place too long, or is significantly dehydrated. Basically, the triggering stimulus produces a simultaneous increase in parasympathetic tone (decreased heart rate and contractility) and withdrawal of sympathetic tone (low blood pressure) that may cause fainting.
Answered 8/2/2012
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