Which action should a diver take when feeling symptoms of DCS?

When a diver experiences symptoms of Decompression Sickness (DCS), the most appropriate response is to breathe 100% oxygen and seek medical attention. This action is crucial because oxygen helps to eliminate nitrogen bubbles formed in the body during a diver's ascent. By breathing pure oxygen, the body can more effectively reduce the size of these bubbles and enhance the healing process.

Immediate medical attention is also vital in cases of DCS to ensure that the diver receives the appropriate treatment, which may include recompression therapy in a hyperbaric chamber.

The other options do not provide effective or safe responses to symptoms of DCS. Simply relaxing and waiting can lead to worsening symptoms and severe complications. Pushing through discomfort is dangerous, as it can exacerbate the condition and lead to further injury. Rapid descent is also highly inadvisable, as it can increase the risk of more serious injuries and does not address the underlying problem of DCS.