Hi. This soudnds like your axoltl is stressed, or "in the mood"
The frantic swimming and refusal to eat sounds like stress, however axolotls aslo do this for periods of time when they want to reproduce. Mine do evry so often during the year. The fact you said it happens on a regular basis makes me think he/she is just frisky and should return to normal.
It could however, be something more serious and you should make sure just in case. It takes a long time for an axolotl to starve to death because they lose weight very slowly. Two weeks in the long run will not make much of a difference like you have noticed in his weight, so do not panic. But it is an indicator that something is up. Has anything changed recently like tempurature or water perameters? DId he eat any new foods. Is he in with any other axolotls? Is the tank in direct sunlight?
I would suggest getting a fresh water master test kit and testing all of the water peramiters. They will give you a good indicator of what water quality is like, and it is bad you can fix it.
In the meantime, whether he be stresses or just frisky, keep offering food calmy like you have been doing. Maybe try a new type of food, something really tasty like a bit of meat. Its only a sometimes food but it may tempt him to start eating again.
