Hello there, I read your message carefully and understood your medical issue. I see you are experiencing episodes of dizziness which are rare and unpredictable, especially while sitting down. Your doctor has decreased the valsartan dosage 80 mg from twice daily to once a day at bedtime. The previous dose was useful in dominating the symptoms until now when the symptom came back. You have had an aortic valve replacement 6 months ago. The use of Valsartan is often associated with orthostatic hypotension, with symptoms of dizziness while sudden sitting. It is more commonly seen while standing up quickly. The very first thing I recommend is to measure your blood pressure (bp), record the results for future evaluation. We want to know the oscillations in your bp while sitting or stretching. Next, as you have an aortic valve replaced 6 months ago, if I was your caring doctor would recommend a further consultation with cardiologist to check if is all fine; further cardiac check up is required then: - ECG - echocardiogram - chest X-ray Until you see your doctor, I advise to: - avoid standing or sitting down quickly; do such movements slowly - keep records of blood pressure and heart rate monitoring - watch what other triggers dizziness apart sitting down: foods? drinks? and report to your physician. Hope this helped. Dr.Albana