The immediate first aid treatment for decompression illness and/or near drowning is:

The immediate first aid treatment for decompression illness and/or near drowning is the administration of 100% oxygen. This approach is based on the principle that providing pure oxygen can significantly aid in the reduction of nitrogen bubbles that form in tissues due to decompression sickness. The inhalation of high concentrations of oxygen enhances the elimination of nitrogen from the body, helping to alleviate symptoms and prevent further complications. In cases of near drowning, oxygen is crucial as it can help restore adequate oxygen levels in the bloodstream, which may have been compromised during the incident.

In contrast, while drinking fluids and resting may aid recovery in other situations, they are not effective immediate treatments for decompression sickness or drowning. Staying warm and dry is essential for hypothermia management but does not address the physiological issues caused by the bends or lack of oxygen. Giving aspirin may provide pain relief but is not a treatment for either condition and does not address the oxygenation or decompression needs that are crucial in the immediate aftermath of such emergencies.