An overheating vivarium is a race you win by removing heat, not by adding cold. Work in order, verify with a thermometer, and only then decide whether the animal itself needs to move. Panicked cooling harms overheated reptiles, so each step below is deliberately gradual.
Remove the heat and open the enclosure up
Switch off the basking lamp and disconnect or turn down any heat mat at its thermostat, rather than relying on the thermostat that may have failed. Open the vents fully, open the enclosure doors a little if the animal cannot escape, and open the room's windows or run a room fan that moves air around the enclosure, not directly into it. Move any portable enclosure out of sun striking the glass, and draw blinds on a window that is heating the room.
Read the thermometer at the animal's level, at both the hot end and the cool end. A single reading beside the lamp tells you little, because the animal's real choice is the gradient. If the cool end is back within the species' normal range, the animal can recover there without being handled at all.
Move the animal only when the enclosure cannot recover
If the whole enclosure has passed the safe ceiling for your species and is not falling, move the animal calmly into a secure, ventilated tub in a shaded room at ordinary room temperature. Support the body fully, place the tub somewhere quiet, and leave the animal to settle rather than handling it repeatedly to check.
Offer drinking water in its usual form, such as a shallow dish, and mist only those species that normally benefit from misting. Never plunge a hot reptile into cold water, never pack ice against the animal, and never spray it with cold water, because a sudden temperature crash can shock an animal that is already stressed by heat. Lukewarm is the coldest anything touching the animal should be, and stillness matters more than speed once it is out of the hot enclosure.
Watch for the signs that mean a vet call today
Call a vet the same day if the animal gapes repeatedly and does not stop once it is cooler, loses its balance, twitches or trembles, cannot right itself, stays limp, or does not return to normal behaviour within a short period after temperatures recover. Those signs can point to problems a vet needs to investigate in person, and a phone call costs nothing beside waiting. Keep the animal quiet and at a steady, moderate temperature while you arrange to be seen, and take your temperature readings with you, because the numbers help the vet judge how serious the exposure was.
Find the cause before the next hot day
An overheated vivarium almost always has a mechanical or environmental cause. Common culprits include a thermostat probe that has slipped away from the heat source, a heat mat running without a working thermostat, sun reaching glass that was shaded in spring, and a room that heats up because doors stay closed on hot afternoons. Test the thermostat with a separate thermometer, reposition and secure the probe, and check that the cool end stays genuinely cool at the hottest time of day.
Before the next hot day, set a simple household routine for heat checks on warm afternoons, so one named person reads both thermometers and records the result instead of everyone assuming someone else looked. KinsLe's Care Teams lets you assign those named thermostat checks to household members and marks each completed check with a timestamp, so a hot-day routine is verified rather than assumed.