Keep in mind that PROGMEM is read-only. You can not change the data in the array at run time.
PROGMEM prog_int16_t accAxisX[][rowSize] = {};
The compiler counts the initializers (and comes up with 0 in this case) to determine the size of the array when you don't provide all sizes. A 0 by 2 array is useless. You might as well delete this whole line.