Jellyfish venom can do more than cause pain; it can also cause anaphylaxis, a severe allergic reaction. Watch the patient for rash, hives, itching, shortness of breath, and swelling. If you suspect an allergic reaction, call 911 immediately or get the patient to a hospital.
Pain from jellyfish stings can last anywhere from a few minutes to several days or even weeks. Nonsteroidal anti-inflammatory drugs (NSAIDS) can be used for pain. Unfortunately, the only sure-fire treatment is time.