What causes night time nausea?

Lots possible here: Vomiting reflex is controlled by 2 units in brain medulla--one receives nerve impulses from GI tract, the other is a chemical receptor. Both have nerve connections to not only GI tract (pharynx, mesenteric vessels, bile ducts) but also from brain corticobulbar areas that mediate smells, sights, & taste. Maybe you have gastritis, but maybe your symptoms have little to do with GI tract. Get checked.