To ease your mind you can always send me to scout and prepare a thorough brief for you on the relative safety of Cancun. I'll require a plane ticket, room at the resort and a few hundred dollars for incidentals.
Just pretend you are in Chicago, LA, NYC or NOLA only half naked, drunk, in a pool and having a ball! You should be fine then.
No worries at all, and we've been to Mexico probably 25 times. Stephanie and usually go out for a run or long walk when we are there, and have never had any problems. That being said, the advice from above is good for travel in any country, including the one you are coming from. You'll have a GREAT time! Welcome to the party!