Yeah, work up to it. It only works if you can sustain it.
First, are you drinking enough fluids? If you are not doing that, you can indeed feel nauseous.
Drink water, tea, or any other non-caloric drink. Avoid artificially sweetened drinks. I drink several sparkling waters like Bubly that are flavored but are not sweetened.
Try herbal teas. Kind of make ritual out of it and try different flavors.
Good luck!
Are you counting your sleeping hours as fasting hours? You should. Example: if you stop eating at 7 pm, go to bed at 11 pm, wake up at 7 am, you have already fasted for 12 hours. By 11 am you will have fasted for 16 hours.