Unlike high blood pressure symptoms, which are poorly defined and often totally absent, low blood pressure symptoms tend to be more upfront and easily recognizable. The development of symptoms is often a warning sign of a potentially serious underlying disorder. Generally speaking, your blood pressure would need to fall pretty dramatically before symptoms develop.

Sodium is a key part of how the body controls blood pressure levels. The kidneys help balance fluid and sodium levels in the body. They use sodium and potassium to remove excess fluid from the blood. The body gets rid of this excess fluid as urine. When sodium levels in the blood are high, blood vessels retain more fluid. This increases blood pressure against the blood vessel walls.
When blood pressure is not sufficient to deliver enough blood to the organs of the body, the organs do not work properly and can be temporarily or permanently damaged. Symptoms of low blood pressure caused by conditions or diseases depend upon the specific cause of the low blood pressure. For example, if insufficient blood flows to the brain, brain cells do not receive enough oxygen and nutrients, and a person can feel lightheaded, dizzy, or even faint.

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.
^ Xie, X; Atkins, E; Lv, J; Bennett, A; Neal, B; Ninomiya, T; Woodward, M; MacMahon, S; Turnbull, F; Hillis, GS; Chalmers, J; Mant, J; Salam, A; Rahimi, K; Perkovic, V; Rodgers, A (30 January 2016). "Effects of intensive blood pressure lowering on cardiovascular and renal outcomes: updated systematic review and meta-analysis". Lancet. 387 (10017): 435–43. doi:10.1016/S0140-6736(15)00805-3. PMID 26559744.
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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