The first step is to get medical attention as soon as possible and contact your supervisor. For emergencies during off hours, contact crew scheduling. They will put you in touch with a supervisor on duty.
From this point forward, take extensive notes and retain copies of all forms and correspondence. If possible, take photographs and seek medical attention within 24 hours of the incident. Even if you do not think you need a doctor, file an incident report to document the event and get the names and phone numbers of any witnesses.