The venom from scats and lionfish is protein based and breaks down with heat. Immersing the stung area in hot water (be careful not to burn yourself) will bring quick relief. Leave the area in hot water for at least 30 minutes. Change the water with more hot water when it cools down. Get someone else to check the water isn't too hot.
The pain should go eventually and then you should monitor the site for infection. Sometimes a bit of fin ray will break off in the wound and can become sceptic. If this happens go to your doctor and have them clean the site.
*NB* the doctor often hurts more than the sting.
Don't worry too much you won't die and only need to seek medical help if you have been stung in the neck, face or chest area. Then the associated inflammation can cause breathing difficulties or heart failure.
eidted to add DON"T USE ICE, it will make it worse