I read in the Miami Herald yesterday that, the other day, when it got down into the 30s here, that iguanas and various other lizards were dropping out of the trees! They even had a picture of a poor, frozen iggy laying on the grass, belly up.
The cold doesn't kill them. Well, it can, but it has to be much colder than that. The cold causes their bodies to slow down, to lose control of all their muscles and fall into a deep sleep. Now, iguanas like to sleep in trees, so when this "hibernation" happens, they simply fall out of the trees. As soon as it warms up a bit, they wake up and carry on.
The article talked about this happening on Key Biscayne, but I also know it happened at Matheson Hammock. My hub works there and saw several iguanas and Cuban anoles (aka Knight anoles) lying around. People were even running them over. Yuck...poor things!