Causes of a drop in blood pressure include impaired circulation, blood loss, infections of the bloodstream and pregnancy due to a rise in blood demand, according to Healthline. Sudden drops in blood pressure can have adverse effects in the body and occur from low or high body temperatures, reaction to medication, severe allergic reaction and dehydration, notes WebMD.
Blood pressure determines the pressure of the circulating blood in the arteries during resting and active phases of each heartbeat. During pregnancy, the circulatory system expands more rapidly than normal, causing the blood pressure to drop. Doctors determine this expansion as a normal condition, and blood pressure is expected to return to normal after delivery, points Mayo Clinic.
Heart conditions such as heart valve problems, extremely low heart rate and heart failure also cause low blood pressure. These conditions prevent the circulation of sufficient blood to various parts of the body. Loss of blood from internal bleeding or an injury can reduce the amount of blood in the body, causing a severe drop in blood pressure. This can also occur from the loss of water from the body and severe allergic reaction, also called anaphylaxis, due to triggers such as insect venom and latex, explains Mayo Clinic.