Blood pressure is the force of blood against the artery walls. Low blood pressure, or hypotension, is a reading of 90 millimeters or less for the systolic blood pressure and 60 millimeters or less for the diastolic blood pressure. Low blood pressure can cause dizziness and fainting and may indicate a serious underlying condition. Severely low blood pressure can deprive the brain and organs of vital oxygen and nutrients leading to shock and eventual death.
Dehydration
A person experiencing dehydration is losing more water than he is taking in. Excessive vomiting or diarrhea, excessive urine output, fever or excessive sweating may cause dehydration. Mild dehydration may cause weakness, dizziness, fatigue and sudden drop in blood pressure. Severe dehydration may cause dark urine, low urine output, a lack of tears, sunken eyes, lethargy and coma. People with dehydration will often have rapid heart rate and delayed capillary refill. Physicians will perform labs to check electrolytes, kidney function and blood count to diagnose dehydration. In cases of mild dehydration, patients may drink fluids and drinks with electrolytes to rehydrate. Intravenous fluids and hospitalization may be necessary for moderate to severe hydration.
Medications
Some medications may cause a sudden drop in blood pressure. Diuretic medications used to help get rid of excess fluids may cause a sudden drop in blood pressure. Medications used to treat high blood pressure may cause patient's blood pressure to drop too low. If a patient takes medications too late in the evening, she may find that she becomes dizzy or even faint when she wakes up in the morning due to a sudden drop in blood pressure upon standing. This is why physicians recommend taking the medication in the morning after waking. Erectile dysfunction medications, particularly in combination with nitroglycerine, can cause an unsafe drop in blood pressure, according to the MayoClinic.com.
Anaphylaxis
Anaphylaxis is a severe allergic reaction and is potentially life threatening. Anaphylaxis occurs when a person encounters a harmless object that triggers a severe histamine response from the immune system. Bee stings, peanuts and latex are examples of common allergies that can trigger anaphylaxis. Anaphylactic shock causes systemic dilation of the blood vessels, leading to a rapid drop in blood pressure. Symptoms of anaphylaxis include wheezing, shortness of breath, throat tightness, cough, chest pain, trouble swallowing, low pulse, dizziness, lightheadedness, shock, hives and loss of consciousness. According to the American Academy of Allergy, Asthma and Immunology, physicians most commonly treat anaphylaxis with epinephrine or adrenalin injections to relieve breathing and circulation problems. Other drugs may include antihistamines such as diphenhydramine to reduce itching and swelling as well as corticosteroids to further reduce the immune response.
