Some of the causes of low blood pressure include:
Getting up after you sit or lie down. This can cause a quick drop in blood pressure called orthostatic hypotension.
Standing for a long time.
Not drinking enough fluids (dehydration).
Medicines, such as high blood pressure medicine or other heart medicines.
Health problems such as thyroid disease, severe infection, bleeding in the intestines, or heart problems.
Trauma, such as major bleeding or severe burns.