and this kind of observation is not mysterious or it is not unique it happens most of the time especially in people who have very low activity and who have stroke the condition your father has is called postural hypotension it is more common in patients taking BP medications BP is high lying down and it goes to very low levels when they stand up and also it cannot cause dizziness so it is not puzzling but constant check up and adjustment of medications is necessary that doesn t mean the medicines are now working or the doctor does not understand also what you can do is make sure your father is fully hydrated he does the regular exercise is the as much as he can passive or active and if that also does not help use you pressure stockings on the legs or even ace bandages around the calves if you have any further questions please let me know him but the one thing you should know is that when he feels dizzy he must sit down and the nearest point to avoid any fall and injury thank you