orthostatic hypotension is primarily caused by gravity-induced blood pooling in the lower extremities, which in turn compromises venous return, resulting in decreased cardiac output and subsequent lowering of arterial pressure. For example, changing from a lying position to standing loses about 700 ml of blood from the thorax, with a decrease in systolic and diastolic blood pressures.The overall effect is an insufficient blood perfusion in the upper part of the body.
in your case bradycardia or antihypertensive medicine are causing orthostatic hypotension
try Lifestyle changes for orthostatatic hypotension -- Drinking enough fluids, such as water; drinking little to no alcohol; avoiding walking during hot weather; and standing up slowly or do some movement of legs before standing . Your doctor may also suggest exercise programs that strengthen your calf muscles, use Compression stockings

HI, thanks for using healthcare magic

High blood pressure at your age would require further investigations. When a person is diagnosed with high blood pressure it can be classified as primary hypertension or secondary hypertension.

Primary hypertension is normally seen in older persons and implies that there is no condition causing the high blood pressure.

Secondary hypertension may be seen in younger persons, in this case, there is another condition which is causing the increase in blood pressure. This could be an abnormal level of various hormones, kidney disease, medication, related to some sleep disorders.
Blood tests and in some cases, urine tests for some hormones, are necessary to rule out a secondary cause.

The dizziness on standing may be due to a fall in your blood pressure when you stand, this can be checked by taking your blood pressure in the sitting and standing position.

You should consider visiting your doctor to be assessed for secondary causes of hypertension, your sitting and standing blood pressure can be done at the same time.

I hope this helps