People who train a lot get good at overriding signals, which is useful in the surf and a problem in a clinic. Here is a practical sorting.
Ignore, mostly. Diffuse soreness a day or two after unfamiliar work. Stiffness in the first steps of the morning that eases within ten minutes. Aching that warms up with movement and settles afterwards. These are ordinary and they do not need an appointment.
Act on. Pain that is worse after activity than during it, and the next day rather than immediately — that is the tendon pattern and it does not resolve by pushing. Pain in one spot you can put a finger on. A joint that gives way or catches. Anything that has changed your technique without you deciding to. And pain that has been there more than six weeks without improving.
Stop and see a doctor. Pain with swelling and heat. Pain with fever. Numbness, pins and needles or weakness. Chest tightness or breathlessness on exertion — that is not fitness, that is a cardiology question. A headache that arrives in seconds. And any pain after a significant impact, particularly a head knock.
The one most often overridden around here is the tendon pattern, because it feels better once you are warm and worse the next morning, so people keep going for months. Catching it early makes a considerable difference. We are in Freshwater, ten streets from Balgowlah and about twenty from Manly.