On 7/2/2021, 28y.o. female patient presented to the pharmacy with her husband to receive their COVID-19 vaccines. Patient was checked in, screened and requested Janssen vaccine.  RPh stepped outside to speak with patient about the potential side effect risks with Janssen due to her age group but told patient ultimate decision of which vaccine to receive was her choice.  Patient stated she wanted to stick with Janssen and RPh then proceeded to review the questionnaire with patient that she had filled out online.  Patient answered no to all questions including the question about ever having a reaction, fainting or feeling dizzy after a vaccine. She was counseled by the pharmacist of potential side effects and how to treat at home or seek medical attention , v-safe program reporting, vaccine card, waiting 15 mins in pharmacy area to be monitored, etc. Her vaccine was administered at approximately 10:12 by rx tech and a wait time of 10:27 given to pt.    Work continued in the pharmacy and the patient and her husband were in the waiting area chairs in front of the pharmacy talking (per him, they were joking about side effects when she started to slump over and he thought she was playing around until she started falling backwards and he tried to catch her by her shirt). At approximately, 10:19, the pharmacist and techs heard a loud noise as patient experienced syncope falling backwards hitting the back of her head on the cement floor and the chair fell out from under her and crashing against the floor. Husband was by her side as RPh ran out to assist asking techs to close the pharmacy down for the medical emergency and to call 911 ASAP, call in around 10:19. Code white was called as well.    Assessment following Adv Events protocol: Patient was breathing and awake with dazed/glazed eyes as pharmacist started trying to ask questions to assess her conscious level.  After about 30-45 seconds pt came back around and answered name and DOB for pharmacist who was talking back and forth with 911 operator.  Patient answered that she felt hot, dizzy and anxious to rph who immediately had cold compresses (cool, wet paper towels) for patient's face and neck. Patient also stated that she had not had anything to eat since 7/1 PM as they had planned to grab breakfast after their vaccines.  Store managers arrived as well.  Local firefighters from the station just down the street were in the store doing their daily meal shopping and heard the call come across to EMS so they came back to the pharmacy to help.  They already had equipment in hand and recorded vitals while RPh was still attending to pt and 911 operator. at 10:24; bp:124/92, pulse 70, O2 sat: 98.  Patient stated she felt well enough to try to sit up in the chair again and get off the hard floor and was assisted up by firemen and husband.  One of the firemen and RPh assessed the back of the patient's head and no blood or knot was located, patient able to ambulate head and neck and no blood was found on the floor.  Patient still able to answer questions, knew where she was, what she had done except in the moment of fainting and knew who her husband was.  Patient refused to be transported to the hospital and EMS was cancelled by firemen to 911.  Firemen left scene.   Rph, rx tech and Assest Protection completed initial questioning for VAERS/SCRT, Incident and EOC contacted while patient and husband still present.  Patient asked for some water and was provided her wishes.  Rph continued to ask patient questions about how she was feeling as reports were being gathered. Patient stated she thought not eating and her anxiety got to her causing her to faint and still reported no previous issues with receiving vaccines.    Also counseled on signs/symptoms of a concussion, soreness to be expected over the next few days and to seek help immediately if any conditions worsened.  Patient was given RPh's card and told that she would be followed up with Friday PM at COB and Monday, but if anything changed between then to call RPh at the number on the business card.  Upon finishing reporting and standing, patient stated back of right knee was hurting from tangle with chair upon fall; otherwise felt fine just a little tired and laughing.  A wheelchair or electric cart was offered to patient upon leaving but she asked to walk out assisted by husband and was released.    Reporting: Pt meds tri-sprintec and lexapro 20mg, no allergies, only medical condition is anxiety, no PCP