How do you recover after a stomach bug?

My young son has ARFID and is already underweight. He is currently recovering from a stomach bug where he vomited many times over the course of two days. He is now holding down liquids just fine and his fever is gone but he's refusing to try any foods. Some of his safe foods are those on the BRAT diet (rice/bread/applesauce), but he says he is too afraid he will throw up. I'm very concerned that we've slid even further backwards on his feeding struggles. He already attends feeding therapy. If you have a fear of vomiting is there anything that has helped you?