The causes of high blood pressure vary. Causes may include narrowing of the arteries, a greater than normal volume of blood, or the heart beating faster or more forcefully than it should as with anxiety issues. Any of these conditions will cause increased pressure against the artery walls. High blood pressure might also be caused by another medical problem. Most of the time, the cause is not known. Although high blood pressure usually cannot be cured, in most cases it can be prevented and controlled.
if it is sudden onset, you'd suspect something hormonal. If it is a rather big jump in BP, and the hypertension doesn't respond to medication, you'd first look at the kidney - looking at renal stenosis (a blockage in a kidney artery) which results in too much renin and aldosterone hormone. An MD would listen there for a bruit. If not that, then maybe a kidney infection, which can be tested in the urine
The other hormone as a culprit would be adrenalines, as in a pheochromocytoma or super stress.
I myself have a sudden onset hypertension which I believe resulted from a virus - and that virus hamper the way that my artery lining (the endothelium) functions. But that seems to be very rare.
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