Thanx for writing your query.
The symptoms which you mentioned are postural related to change in posture. This is called as postural hypotension
. It is usually seen in old age & also in diabetic.
This is related to sudden change is posture that is from sitting to standing leads to drop in blood pressure.
All you can do is get your blood pressure checked in lying down than sitting & than in standing position & confirm the drop in blood pressure.
All you need to do is gradually & slowly change your posture. This simple technique allows body to adjust to new posture.
Wish You Good Health.