Which of the following is an emergency requiring a visit to the ER or hospital?

A temperature of 95 degrees or lower measured rectally is considered hypothermia, which is a dangerous condition that can lead to serious health problems, including organ failure or death if not treated promptly. This condition requires immediate medical evaluation and intervention, often in an emergency setting, to prevent further complications.

In contrast, a headache, while it can be severe and potentially a symptom of a more serious condition, does not automatically warrant an emergency visit unless accompanied by other alarming symptoms. Slight bruising typically suggests a minor injury and does not require emergency care. Seasonal allergies are generally manageable with over-the-counter medications and do not necessitate a visit to the ER. Therefore, the critical nature of a dangerously low body temperature justifies the need for emergency medical attention, making it the correct choice in this scenario.