Hello! Thank you for the query. What you have experienced is most likely orthostathic hypotension. This is more a reaction than a symptoms of any disease however it can indicate some diseases. It is caused by sudden blood pressure drop due to sudden stand up. As a result, not enough of blood gets to the brain and gives symptoms like yours. This reaction is very common in healthy people. However it can also appear (if not present before) with some diseases like: arterosclerosis (mostly in cervical arteries), heart issues, diabetes, Addisons disease or simple dehydration can be a reason of it. And so can be your medicines. I suggest you to visit your doctor and have some tests performed. Heart ECg, stress test, heart ultrasound, tilt test, Dopplers ultrasound of cervical arteries should be considered. Hope this will help. Regards.