Guessing at the usual FA decision tree here, and the assumption of horses rather than zebras.
1. Is it an ABC (airway-breathing-circulation) issue? If so, doctor consult is necessary, whether doctor is on plane or the co-pilot contacting the airline's contract telemedicine company on the ground to determine appropriate actions.
2. Do symptoms indicate an acute NEED to place passenger near toilet?If so, move passenger closer.
3. General nausea in absence of other symptoms- presume the horse is drunk or hung over, offer non-prescription headache tablet/anti-nausea med from plane medical kit