What is hierarchy? Answer Wiki. A hierarchy is A body of persons or things ranked in grades, orders, or classes, one above another; specifically in Natural Science and Logic, a system or series of terms of successive rank (as classes, orders, genera, species, etc.), used in classification.  From the OED .
1 During the first 24 weeks of pregnancy, it's common for blood pressure to drop.  A decrease in blood volume can also cause blood pressure to drop. A significant loss of blood from major trauma, dehydration or severe internal bleeding reduces blood volume, leading to a severe drop in blood pressure.
This is an indication that insufficient blood flow is reaching the brain. This, in turn, can lead to weakness, nausea, confusion, and blurry vision. Low blood pressure can affect other organs leading to shortness of breath, fainting, blacking out, chest pain, and cool, clammy skin. What Are the Causes of Low Blood Pressure?