My wife got stung last year in July, while we where on a cruise and swim boat trip. Apparently it was very bad year for Jellyfish in the Med.
The staff on the boat where fully prepared.
If you do get stung then DON'T touch or rub the area you will make it worst. Wash the area with fresh water as this kills the stinging cells. Then wash it again with Vinegar, this neutralises the sting and kills the pain, then rinse it again with fresh water.
Hopefully this year it should be back to normal and you won't need to do any of this, but it's best to know what to do just incase.
By the way the pain is similar to stinging nettles so it's no big deal anyway.