If I work too hard and find it difficult to breathe underwater, I should...

When you find it difficult to breathe underwater, the best course of action is to stop all activity and rest. This allows your body to recover and catch up with your breathing. Continuing to exert yourself can lead to increased anxiety or fatigue, which can exacerbate the breathing difficulty and potentially lead to dangerous situations underwater.

Resting gives you time to stabilize your breathing and assess your situation calmly. It's also important to be aware of your surroundings and ensure you are safe while resting. Depending on the conditions and your buddy's proximity, it might also be appropriate to signal your buddy for assistance once you have regained your composure.

While ascending to the surface may seem like a suitable option in some cases, it should not be done abruptly without assessing the situation and ensuring your safety. Proper ascent procedures should always be followed to reduce the risk of decompression sickness.