Has anyone here ever been stung by a jellyfish, trodden on a stone or scorpion fish or been bitten by a sea snake?

If so what treatment did you use to soothe the sting? did it work or did it make the pain more? did you have to have any antivenoms administered?
If not do you know anyone this has happened to or been on the beach and seen someone being treated for marine poisoning?
I have an exam on monday about marine toxins and antivenoms and would appreciate anyones first hand knowlege on the subject, sometimes scientific papers seem a bit impersonal and rarely go into detail regarding pain levels.
I have never been stung myself severely however once had a tiny sting on my cheek whist diving in the north sea. that was pretty painful but nowhere near as bad as it could have been.
Also where were you when this happened?