Hello,
Usually there is a reason for everything you just don't know what it is. Experiencing light headedness may be due to changes in blood pressure. You blood pressure might drop all of a sudden or it may increase. At any rate, the brain doesn't get enough blood at that moment so it doesn't get enough oxygen to fully function. This brings about dizziness and possibly blurred or white vision. It's important to exercise to keep your muscles toned and your cardiovascular system working properly. I suggest you start exercising and possibly start with aerobics or ride a bike if you have one. If this light headedness continues, you need to see a doctor to find out what your problem is. You can check your blood pressure at a local pharmacy for free and your resting blood pressure should be 120/80.