Radiation sickness, also known as acute radiation syndrome, occurs when a person is exposed to a high dose of ionizing radiation in a short period. This exposure can damage cells and tissues, leading to a range of symptoms. Common signs include nausea, vomiting, fatigue, and hair loss, which can appear within hours or days after exposure, depending on the dose received. The severity of radiation sickness depends on the amount of radiation absorbed and the duration of exposure. In severe cases, it can lead to serious health complications, including damage to the bone marrow, which affects the body's ability to produce blood cells, and can ultimately be life-threatening.