Final answer:
The medical assistant's first action when a patient feels faint should be to lay the patient flat on their back to prevent fainting by aiding blood flow to the brain.
Step-by-step explanation:
If a patient sitting on the examination table complains of feeling faint, the first action a medical assistant should take is to assist the patient to a supine position. This means helping the patient to lie flat on their back, which can prevent them from fainting by improving blood flow to the brain. Options such as placing a pillow behind the patient's back or moving them to a chair may not provide immediate or adequate prevention against fainting, and administering oxygen without assessing for hypoxia or having a physician's order could be inappropriate. Ensuring the patient's safety by lying them down is the most immediate and appropriate first step to take in response to their symptoms.