Benadryl is often given for motion sickness and nausea. I have a rare connective tissue disorder and one of my symptoms is chronic nausea and vomiting. Part of my regimen for controlling the nausea is Benadryl (or hydroxyzine) twice a day. Nausea control is a side effect of the Diphenhydramine.
From WebMD: Diphenhydramine is an antihistamine used to relieve symptoms of allergy, hay fever, and the common cold. These symptoms include rash, itching, watery eyes, itchy eyes/nose/throat, cough, runny nose, and sneezing. It is also used to prevent and
treat nausea, vomiting and dizziness caused by motion sickness. Diphenhydramine can also be used to help you relax and fall asleep.
https://www.webmd.com/drugs/2/drug-5680/benadryl-oral/details