At approximately 9:45 PM I experienced sudden onset of vasovagal syncope. I became unconscious and my housemate contacted first responders. My housemate described that I shook and appeared like perhaps I had a mini seizure.  Details as written by me on 01/04/2022  Had 8:55 AM appointment to receive Pfizer booster vaccine no. 3. It had been since late February that I received my second dose. Upon receiving vaccine, I was laid down and the injection was deposited in my upper right arm. I felt pressure and a sensation, mild numbness down my left arm right after this happened which soon disappeared. The nurse had me wait 5 minutes in the room where I received the vaccine and then she had me wait ten more minutes in the room where patients are observed post-vaccine. I came home and had a smoothie with lots of healthy ingredients. I also grabbed a large water bottle and added some mineral drops to it, planning to drink that all throughout the day. I did take my Thyroid medicine but unlike usual, I kinda took it with food. (You?re supposed to wait 30 min) but I had to rush off to work and figured that would be better than not taking it. My day after that proceeded energetically, I was able to accomplish a lot at work and went for a brisk 30-minute walk on my late lunch break in the afternoon. I had chicken and veggies for lunch. I didn?t have much for dinner, just some fruit, five or six guavas from a friend to tide me over. I drank lots of water and herbal tea throughout the day. After work I felt energetic enough to stop by a Monday night fellowship group that I sometimes attend. Towards 8 PM I started to feel a little tired and left the group early so I could prepare to go home, take a bath, and get some rest ? expecting vaccine symptoms (chills, fever, etc.) to kick in sometime in the night. At the fellowship I noticed I was a bit more ?shivery? than usual, and my arm as tender to the touch. When I got home, I puttered around the kitchen (drank some water, and ate the rest of my guavas) while my roommate talked to me about her day. She went to bed after 9 PM and after a little while I decided to get ready to take a warm bath with Epsom salt thinking this might ease potential oncoming muscle aches. I turned on the water, and thought I didn?t feel bad, just a little tired ? which is usual for me. I did feel that my arm was hurting a bit but not in such a way that I couldn?t bear it. For some reason, I had a brief thought that ?passing out in the tub would be pretty horrible? but thought to myself that ?I should be fine.? I decided I should get some ibuprofen in my system for the tender arm so that the dull ache of pain didn?t get much worse and made my way to the kitchen. As soon as I was in the kitchen, I knew I was going down. I managed to get to my roommate?s bedroom door a few steps away and knocked on it saying that I was going to faint while trying to get myself in a seated position to avoid fainting. She said I blacked out and had a ?mini-seizure? where my body arms and legs all went straight. I was only wearing a towel! I was soon awoken from what felt like a long, deep dream, it took a moment to reorient to where I was and what had happened. I felt incredibly strange. My arms and chest muscles felt really, really tense like they had seized up and my hands were tingling, this lasted a couple of minutes. I was breathing hard and sat up to put my head between my knees feeling like I might pass out again. I rocked back and forth for a while breathing deeply. I directed my roommate to call 911 and get me some clothes. I think it was close to 10 PM by this time. The first responders came and they checked my vitals and and everything including blood sugar levels checked out within normal ranges. Blood pressure was 120 over something, maybe 70? I don?t remember. I felt most comfortable on the floor and did not want to sit in a chair for fear of falling. An ambulance came and those responders checked my heart, and that was normal too. I was told that I could go to the ER if I wanted and could get labwork and stuff done if I wanted, they could take me or someone could drive me. I signed off that I would stay home and wait things out. I was feeling much more stable, still exhausted and a little wobbly but not at all what I felt like when I woke up from fainting. My roommate?s boyfriend came to stay the night on the couch, just in case I had further symptoms. I took one advil and drank some cool water and ate a couple salty cashews. I slept on the floor where it felt safe to be, I didn?t get much sleep there, but I did get some. When I woke up I went to the bathroom and had much more pee than normal. I?m not sure what that was about. I drank a lot of water the day before but pretty sure I had gone to the restroom before bed. Today I?ve been resting a lot and took a long nap in the afternoon which felt good. I feel a little achy and tired and have been running about a 99 degree fever, and earlier in the day it was closer to 100. In the evening I was able to get up and do some cooking. Will probably go to bed a little bit early. This morning I called my Dr.?s Office and they took down the message about what happened to me to pass along to the doctor. They have put me on the waitlist to come in if an appointment opens.  To note, my last cycle ended Dec. 24 and so I am in the more level hormonal part of the cycle. Also to note, I do have a history of vasovagal responses due to the sight of blood, receiving blood draws, and to pain (several broken bone experiences.) I have also passed out twice due to heat regulation issues during my menstrual cycle, usually this happens if it is abnormally hot and humid when I am on the first day of a period. I would say that I have a mildly anxious but levelheaded disposition about things. I did not expect to pass out in this situation. Only one other time have the ?seizure-like? symptoms been noted as part of the fainting experience. I also tend to have low blood pressure. In the past I was observed for heart rhythm problems and a monitor revealed that sometimes my heart will ?skip? a beat, not significantly enough that I need to treat it, this issue has also seemed to not be of concern since I started the Thyroid medication. I have never had a vasovagal response to a vaccine.