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is an antisympathetic drug and acts by relaxing smooth muscles of urinary bladder
and prostate. However due to cross actions on the cardiovascular muscles it can result in low blood pressure (hypotension
and other side effects. Using antihypertensive drug can worsen these cardiovascular effects. Worsening effects is proportional to number, type and dose of antihypertensive used.
The episode of hypotension is probably due to this phenomenon. Hypotension can result in reflux changes such as increased heart rate
to compensate for low blood pressure. In addition adrenal surge which is associated with hypotension can produce heart increase and increase in blood pressures.
Hence I would suggest you to follow your doctor's suggestion. Monitor your pulse and heart rate. Your doctor can then make adequate changes and prescribe you proper medications suitable in this context.
Hope this helps.
Wish you good health.