I suspect you mean the Z position.
For the position of the nozzle relative to the bed, the axes are (+ / -):
X = right / left
Y = back / front*
Z = up / down*
The Z position is usually a open loop control based on the movement of the stepper motor(s). The initial position of the bed is usually set either by a limit switch (a microswitch) or be an autoleveling sensor (Usually a BLTouch) any of these can go wrong.
*. For printers that move the bed rather than X carriage, so + (=‘up’) means moving the bed down. Usually the Y direction is done by moving the bed, so + (=‘back’) means moving the bed toward the front.