Jellyfish Stings: There are over 200 types of jellyfish. Some are not poisonous, however, some are very poisonous and may lead to coma or death. Symptoms of a jellyfish sting include stinging pain, rash, itching, and raised welts. More serious symptoms include nausea, vomiting, abdominal pain, diarrhea, or muscle spasms. Treatment depends on the type of jellyfish. Some may require immediate hospitalization.