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.
1 Feel dizzy or lightheaded. 2  Feel short of breath and find it harder to exercise. 3  Feel tired. 4  Have chest pain or a feeling that your heart is pounding or fluttering (palpitations). 5  Feel confused or have trouble concentrating.  Faint, if a slow heart rate causes a drop in blood pressure.