1 Low blood volume shock (hypovolemic shock). 2  This is one of the most serious, and sometimes life-threatening, complications of dehydration. 3  It occurs when low blood volume causes a drop in blood pressure and a drop in the amount of oxygen in your body. It occurs when low blood volume causes a drop in blood pressure and a drop in the amount of oxygen in your body. 2  Kidney failure. 3  This potentially life-threatening problem occurs when your kidneys are no longer able to remove excess fluids and waste from your blood. 4  Coma and death.