Serious medical conditions that cause lightheadedness include dehydration, shock, heart disorders and internal bleeding, according to Healthline. Allergies, altitude sickness, colds, low blood sugar and over-the-counter medications also cause dizziness. When symptoms of a heart attack or massive blood loss accompany the lightheadedness, the condition requires emergency care.
Lightheadedness is a dizzying sensation in which a person feels like her head is not getting enough oxygen and that she might faint, explains Healthline. To prevent lightheadedness that is not a result of underlying medical conditions, a person should drink a lot of water, stand up slowly, and avoid alcohol and sedatives. If the condition persists or appears in combination with other more serious symptoms, it is important to seek medical assistance to determine the cause and receive treatment as needed.