F900 has it nearly right, but do not over tighten your shoulder straps. It is the lap straps that hold you in the seat and certainly for serious negative these should be as tight as you can possibly get them, shoulder harness basically stops your body moving forward and hitting the panel and this should just be comfortably tight or you compress your chest and it can make things worse if you are feeling airsick.
I suspect the truth is though that you are not experiencing negative G, that is unusual in normal operations but reduced positive G can still be unsettling and even here being properly strapped in will help.
Last edited by foxmoth; 8th April 2013 at 20:12.