Hi & Welcome. You seem to have developed fall in BP (hypotension) after changing the medication. The combination of Lisinopril (20 mg) with Hydrochlorthiazide (12.5 mg) is generally prescribed to lower the high BP which is not controlled by Lisinopril alone. You are advised to consult your treating doctor to kindly review the prescribed medication, probably your BP could be controlled with Lisinopril alone along with certain lifestyle changes such as reduced dietary salt intake and stress, daily exercise, avoid red meat, fatty meals, etc Hope this will help.