Which of the following symptoms indicates the possibility of a convulsion due to oxygen toxicity?

Nausea can indeed be a symptom that indicates the possibility of a convulsion due to oxygen toxicity. When divers are exposed to higher partial pressures of oxygen, as is common when using enriched air nitrox, they may experience a range of physiological effects. Nausea is one of those effects and can be an early warning sign of potentially more severe conditions such as oxygen toxicity, which might culminate in seizures.

Oxygen toxicity occurs when the body is exposed to an increased level of oxygen for a prolonged period, leading to adverse effects on the central nervous system. As the body's systems react to the changes in oxygen levels, symptoms can develop that signal a need for immediate attention or a change in breathing gas mix.

The other options listed—excessive sweating, difficulty breathing, and fatigue—are not typically associated specifically with convulsions from oxygen toxicity. While they can occur in various diving scenarios and may indicate stress or discomfort, they are not specific indicators of the onset of seizures related to oxygen toxicity. Recognizing nausea as a possible precursor is crucial for divers using enriched air, as it allows for early detection and corrective measures to avoid severe complications.