what causes light headedness?
A lot of things. The most common is if you get up too fast after being sedentary, your heart is in a relaxed state and not ready to start working harder.
You can also get light headed from low blood sugar.
A third common cause is something known as syncopy. For unknown reasons, when you go to the bathroom, your body restricts blood flow to your legs. Sometimes this mechanism malfunctions and can cause light headedness or even fainting.
not eating enough...pregnancy...low blood pressure...anaemia...lots of things really.