Many people (myself included) dislike the vanilla nausea effect in that it causes headaches / sickness while looking at it. This mod allows you to replace the nausea effect with something else or just completely remove it.
When you first install the mod on your client it will be in mode 1, instead of the swirling nausea effect your controls for left and right will be inverted. In the NoNausea.cfg file you can change the mode to one of these:
0: The nausea potion effect will do nothing.
1: The nausea potion effect will invert your controls for left and right.
2: The nausea potion effect will invert your controls for left/right and forward/backwards.
3: The nausea potion effect will slightly tilt your camera.