Light headed sensation when standing up from sitting or lying position may be quite normal for a lot of people, especially young female. This is called postural hypotension. Management usually consists of being aware of the issue and more cautious when standing up.
Some people may feel light headed (or even faint) AFTER exercise or after prolonged standing still. This is called vasovagal attack. There is no specific medical treatment for it other than to be aware of it, to take steps to avoid situation that may provoke the faint/light headed sensation, and immediately lie down when the attack comes (to prevent injury). Isometric contraction may also help in some.
For both the above, one should keep well hydrated, and avoid unnecessary hunger. Simple tests may be needed: blood pressure, ECG and hemoglobin.
The following are features that may warrant seeing a cardiologist:
1) faint while sitting or lying down
2) faint DURING exercise
3) faint with associated cardiac symptom (palpitation, chest pain or shortness of breath)
4) family history of unexplained death at young age (<40 years old)
5) personal history of significant cardiac disease (eg. congenital heart problem, previous heart attack/stenting, heart failure, etc)
6) faint without warning
