Altitude sickness, also known as acute mountain sickness (AMS), occurs when a person ascends to high altitudes too quickly. At elevations above 8,000 feet (2,400 meters), the air pressure decreases, leading to lower oxygen levels. Symptoms can include headaches, nausea, dizziness, and fatigue, as the body struggles to adapt to the reduced oxygen availability. To prevent altitude sickness, it is important to ascend gradually, allowing the body time to acclimatize. Staying hydrated and avoiding alcohol can also help. In severe cases, descending to a lower altitude is necessary, and medical attention may be required for serious symptoms.