HI Elaine,
1/ As suggested by Jane, your seat belt should hold you secure if it is serviceable.
2/ The fact that you get a pain whenever this happens is not good and you may have an underlying medical problem that should be addressed.
3/ Tell your husband that road awareness should reduce the amount of times that he has to "slam the brakes on" and that he may want to attend an advanced drivers course to help him drive more "smoothly".
Cheers now
Oldgrubber
July 2019