Hi Samantha, Welcome to HealthcareMagic Forum.
How old are you? Are you Diabetic or Hypertensive? Are you on any medication? You are having what is called as Postural Hypotension
wherein low blood pressure happens when you stand up from sitting or lying down, where you can also faint. Have you fainted anytime? If you have mild episodes, you may not need treatment. Many people occasionally feel dizzy or lightheaded after standing and it is usually not a reason to be worried about. The treatment for more severe cases depends on what is causing your episodes of low blood pressure. You may want to see a Physician so that he may evaluate you and rule out the cause and prescribe blood pressure increasing medications. In the meantime, you can do some lifestyle changes, Drink plenty of water, avoid alcohol and walking during hot weather, stand up slowly when you want to . Your doctor may also suggest you exercises that strengthen your calf muscles which are called peripheral heart. If you are not hypertensive, he might suggest increasing the amount of salt in your diet. You can also wear Compression stockings. Avoid bending at the waist and If you get dizzy while standing, sit down and cross your thighs in a scissoring fashion, squeeze and lean as far forward as possible. This will encourage blood flow.
Wish you Good Health.