A blood pressure of 90/60 mmHg is in the low limit of normal. There are many causes. For example, hypovolemic shock, overdose of antihypertensive drugs, postural causes.
Hypovolemic shock can be characterized by a large drop in blood pressure. Clinical causes of shock include: massive blood loss, massive fluid loss, massive burns, infections, severe trauma, cardiac dysfunction, allergies, and intense neurological stimulation.
Overdose of antihypertensive drugs in hypertensive people can also lead to a significant drop in blood pressure compared to before. This is mostly seen in elderly people with memory loss.
Postural blood pressure drop. Prolonged lying down or sitting position suddenly stand up can cause a large drop in blood pressure, but mostly transient, can be combined with dizziness, blackout.
In addition, a long period of time without food or water may also cause a drop in blood pressure.
A sudden drop in blood pressure from the baseline level should be taken seriously and, if necessary, prompt medical attention should be sought to identify the cause and rationalize the diagnosis and intervention.