We did some snorkling in the Yucatan cenotes as well. Amazing.
At one point I drifted to the left, instead of directly following my kid. I ended getting caught under the top of the cave. Let me tell you, that was a tense few seconds. After the initial panic (let's say 3 seconds, felt like a minute) subsided and I got back in control, I started to touch the top and pull myself back to the center. Fortunately, the guide company has an extra guy whose sole purpose is to save the lives of the dumb touristas. So he hauled me back into the center so I could breathe again.
I've done a little scuba in the Caribbean, I don't have the cojones to contemplate cave diving.
BTW - plug for an amazing tour company:
Alltournative Adventures. Very sustainable, employ locals and encourage them to build businesses, such that their family members that once were in El Norte, are returning home. In the Rivera Maya, they use Unimogs on some of the tours - very cool! I *hate* organized tours. With this group, I'd consider choosing a destination based on where they were locatedl.