While it is easy to assume that axolotls sleep during the night, this is actually very incorrect. These salamanders will sleep throughout the day as well, especially after a long period of hunting and exploring. They will hide in caves, behind rocks or plants in the aquarium, and remain very still for a long time. They will also show lower gill movement, as their oxygen requirements are less during their resting state. Their colors will be paler as well, and they will appear almost ethereal in appearance.
The main reason why it is so challenging to tell if your pet axolotl is sleeping is that they do not close their eyes and fall into a deep sleep like most animals. They simply retreat to their favorite hiding place or habitat and remain very quiet, with a very pale body color and lower gill movement. This is how you know that your axolotl is asleep or at rest, and you should not disturb them until they wake up.
To provide your axolotl with the best possible environment, you need to make sure that they are getting enough sleep. This will mean ensuring that their aquarium is placed in a room with dim to no light, which is more similar to their natural habitat at the bottom of deep waters free from direct sunlight. You should also provide them with plenty of hiding spaces, and keep the water temperature at the optimal level. Changing the water temperature too much can have adverse effects on these salamanders, as it may lead to fungal infections or ammonia spikes, and this is something you should avoid at all times.