"The symptoms, however, gradually become apparent and then more and more intense in the following 5 to 120 minutes (30 minutes on average). Irukandji syndrome includes an array of systemic symptoms including severe headache, backache, muscle pains, chest and abdominal pain, nausea and vomiting, sweating, anxiety, hypertension, tachycardia and pulmonary edema. One unusual symptom associated with Irukandji syndrome is a feeling of "impending doom". Patients have been reported as being so certain that they are going to die that they beg their doctors to kill them to get it over with. Symptoms generally abate in 4 to 30 hours, but may take up to two weeks to resolve completely."
"Even under the "maximum dose of morphine," Teresa remarked that she "wished she could rip her skin off," and is later seen writhing uncontrollably from the pain while lying on her hospital bed. In one scene, Teresa's feet are shown contorting and digging into the bed, and she's wiggling her toes and kicking her feet around. When the camera moves back, Teresa is seen rubbing her face, her body is contorting in agony, and her legs are rapidly sliding and kicking around on the bed. Jamie, at his worst, is also seen writhing in pain, curled up in a ball and barely able to speak. Jamie said he wished that he was stung by Chironex fleckeri instead since "the pain goes away in 20 minutes or you die.""
tl,dr: You usually don't die, but you wish you would.