Sometimes, when I stand up my sight goes black and I feel very dizzy. I have to sit back down again until my sight clears. Why is this happening?
Standing up quickly can cause blood pressure to drop which can lead to the sort of symptoms you describe. Elderly people and young women are particularly prone to this and often find that standing still for long periods may produce the same feeling. If you have been lying down or sitting still for any length of time, make sure you rock your feet back and fore before standing up. This will contract and relax the calf muscles and help to get the blood pumping back to your heart. Fidgeting if you have to stand still will have the same effect and should help prevent these dizzy spells but if they persist despite this then make an appointment to see your doctor and get this checked out.