Anyone can develop hypotension, but certain groups of people are more likely to experience it, and there are different types. For instance, orthostatic (positional) hypotension, which occurs when you stand up after sitting or lying down, is more common in older adults. Typically, “your body has certain compensatory mechanisms to prevent your blood pressure from falling when you stand up,” explains Willie Lawrence, MD, an interventional cardiologist at Research Medical Center in Kansas City, Missouri, and a spokesperson for the American Heart Association. But, he adds, “orthostatic hypotension is a problem for some people because these reflexes that should occur, don’t occur.”
Pulse pressure (the difference between systolic and diastolic blood pressure) is frequently increased in older people with hypertension. This can mean that systolic pressure is abnormally high, but diastolic pressure may be normal or low a condition termed isolated systolic hypertension.[59] The high pulse pressure in elderly people with hypertension or isolated systolic hypertension is explained by increased arterial stiffness, which typically accompanies aging and may be exacerbated by high blood pressure.[60]
Low blood pressure is also known as hypotension. This is usually defined in an adult as a systolic recording of less than 90 mmHg, although it has been suggested that for elderly people, below 110 mmHg is a more appropriate definition. Blood pressure and heart rate are controlled by the autonomic nervous system (the nervous system that controls bodily functions that we do not have to think about).                                                                                                                                                                                                
Allergic reaction (anaphylaxis): Anaphylactic shock is a sometimes-fatal allergic reaction that can occur in people who are highly sensitive to drugs such as penicillin, to certain foods such as peanuts or to bee or wasp stings. This type of shock is characterized by breathing problems, hives, itching, a swollen throat and a sudden, dramatic fall in blood pressure.
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