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The new drug has not been named / Is the old one LISINOPRIL?
is common at this age even without drugs.
Autonomic imbalance is quite common.
Blood pressure needs to be checked lying and standing.
Vasodilating drugs may worsen this.
First dose effect - some times drugs like diuretics may have a dramatic effect after first dose...
The treating Internist is the one, who will be able to assess and assist further.
Wishing speedy recovery