My checklist would be the following:
1) What are my parameters like? If I have done a water change very recently, have I cleaned up all the poop I can see? Is my axolotl a 'sensitive' axolotl that reacts to very small changes in water chemistry?
2) Is the flow of my filter very strong? (You can divert the flow of some filters by moving the output nozzle so that it points away from the main body of the tank, by placing a tight/pop sock over the inlet, or by affixing a piece of clean sponge to the outlet so that water can still get out).
3) Do I have adequate hiding places?
4) Is my tank cool enough?
5) Does my axolotl show other signs of illness, such as spots, fungus or wounds?
6) Do I ever use the tank light? Is it very bright? If not, do I have adequate cover from the room's lights?
If all of these are apparently okay, then I would question whether the axolotl has simply matured. I find that some axolotls' gills will curl naturally - some axolotls have very large gills which curl backwards, others simply seem 'curly.' The relaxed behaviour sounds like the natural 'mode' of a juvenile growing into adulthood. Axolotls also sometimes 'freak out' momentarily when scared - a light is suddenly turned on, someone moves suddenly, or something falls over, and the axolotl is momentarily scared. I have an albino that sometimes has crazy moments for no apparent reason (think dogs that get 'wind up their bottoms' and suddenly start acting a bit hyper).
Hope this helps!
