What symptom is commonly associated with seasickness?

Nausea and discomfort are hallmark symptoms of seasickness, which is a common condition experienced when a person is in a moving vessel. This condition occurs due to a conflict between the brain's balance systems. As the body experiences the motion of the boat, especially in rough seas, the inner ear and visual perceptions may send mixed signals to the brain, leading to the sensation of nausea. Individuals may feel uneasy and experience a general discomfort in their stomach, which can be exacerbated by additional factors such as anxiety or the specific motion of the vessel.

In contrast, increased energy and a sore throat are not typically related to seasickness, as this condition is associated with a lack of energy and gastrointestinal distress. Headaches can occur but are secondary to the primary symptoms of nausea and discomfort. Hence, the presence of both nausea and discomfort is most indicative of seasickness, making this the correct choice.