Try not to rush suddenly; get up slowly out of bed or out of a chair. Make sure you eat regularly. If necessary carry biscuits or fruit with you to eat if you are somewhere food is not readily availible to you. If you feel faint, try to tell someone so that they can help you, and lie on a couch, bed or the floor on your side as quickly as possible, breathe slowly and deeply, until you feel better then try to get up slowly and perhaps have a sweet drink.