Unfortunately it seems that the particular head bobbing mechanics of SiN makes me quite sick. I've not noticed this in other games..

Anyone know a trick to kill/reduce the head bobbing?

I'm sure there is an option in Settings, isn't there?

EDIT: sorry there isn't. I must have mistaken it for another game.

Go into the console (normally tilde key) and experiment with the following variables.

bob_pitch: The amount of movement that the player's screen moves up and down while in motion. Default 0.002

bob_roll: The amount of movement that the player's screen moves left and right while in motion. Default 0.002

bob_up: The amount of time before the player's screen starts moving. Default 0.005

You should leave them all at 0, or start at 0 and increase them 0.0001 at a time, testing if the movement makes you feel too bad.

Source: Quake II console commands and variables