Nausea can indeed be a symptom of elevated ACh.
Yes, fisetin should work fast; if it does anything for you, you'll know within the first couple of days.
Good luck.
I am increasingly of the view that diet and lifestyle should be first addressed before messing with any additional supplementation. Those were the changes that netted the greatest overall benefits for me, even considering the great results I've had from this stack or things like NSI-189 or vorinostat.