The causes of low blood pressure may include heart disease, dehydration, and the use or allergic reaction to certain medications. Most common with the elderly, sudden drops in blood pressure may lead to symptoms like fatigue, anxiety, depression, or dizziness—especially upon making a sudden change in body movement. In rare cases, treatment is required, usually in the form of medication that helps alter blood pressure receptors or constrict arteries to reduce the likelihood of sudden or frequent drops in blood pressure.