Part of tail drooping to one side

[Axie23]

HI, the part of my axolotls tail which is on top of its back is starting to droop to one side. i the rest of the tail is normal. Does anyone know what this means? i am about to clean its tank just in case that has something to do with it. please note the temperature of its water is quite cold this time of year because it is winter here....

Thanks

 

[Jennewt]

I've never heard of this particular symptom before. Is there a strong water flow from the filter?