Me? First I'd tip my divemaster before I went under for the first dive. At least I know he'll have a thick steak and a nice bottle of wine while I'm freezing my buttocks off.
Second, I'd stick close to my buddies. I'd have them tie into each other so we all survive together.
Third, twenty miles swimming is not an option. When the Coast Guard looks for wayward folks, they follow the direction of the current.
Fourth, inflate your sausage. If you've ever been in a jet or helo looking for someone it's tough--even the smallest wave could block you the split second the searching aircraft is looking right at you.
Fifth, when all hope is lost and you feel like you're never going to make it, start telling jokes. Have a competition to see who can tell the most stupid jokes you've ever heard. My buddy won one contest with, "What's the sickest country in the world?"
Sixth, when the Coast Guard arrives, don't forget to thank them. They risked their life for your safety...or at least you interrupted thier evening of TV and Scubaboard lurking.
Finally, I'd pee all I could....just one less thing to think about...
Oh, and the sickest country in the world....
....Germany.