Which condition is characterized by headache, lethargy, and confusion after mountain ascent?

Acute mountain sickness (AMS) is the correct answer because it is specifically associated with the symptoms of headache, lethargy, and confusion following a rapid ascent to high altitudes. AMS typically occurs when an individual ascends to altitudes above 2,500 meters (about 8,200 feet) without proper acclimatization. The body's inability to adjust quickly to decreased oxygen levels at higher elevations leads to these symptoms.

In contrast, while altitude sickness is a broader term that can encompass various conditions related to altitude, it is not as specific as AMS. High-altitude pulmonary edema (HAPE) and high-altitude cerebral edema (HACE) are more severe forms of altitude-related illnesses that include other symptoms and typically occur after AMS. HAPE is characterized more by respiratory issues, while HACE involves more severe neurological symptoms such as extreme confusion and altered consciousness. Therefore, the hallmark symptoms of headache, lethargy, and confusion point specifically to AMS.