I put COVID-19 Pfizer-BioTech because it made me choose something, but I don't know which COVID shot it was actually. I just know it was a COVID booster.  I received the vaccine at ~9:30 am. Everything else that day went normally. At 2:00 am, I woke up feeling unwell. My arm hurt and I just had an overall sense of malaise and discomfort. I got out of bed to grab something to drink, hoping it would help. I bent over to grab a drink from the bottle shelf of my fridge, and very rapidly realized I was about to loss all vision and also lose consciousness. I get tunnel vision sometimes, but this time happened so quickly that I immediately dropped fully to the group on my stomach. I live alone and was afraid that if I did lose consciousness, I might hit my head and no one would be there to help me. I crawled to the bathroom because I started feeling really unwell. There, I became incredibly nauseated and extremely, extremely hot. I was dripping with sweat, I could feel it dripping in between my arms and my knees and the back of my neck. I laid there on the cold floor for a while, because during my very first COVID vaccine, I experienced the same thing. It was during that initial episode that I learned that staying horizontal and on the cold floor made the nausea and overheating improve, but that staying upright only intensified my symptoms. I writhed around on the floor for awhile, groaning in pain, until the nausea and extreme overheating subsided after ~15 minutes. I returned to bed and woke up again at 6:30 am.  I woke up with a distended lower abdomen and suprapubic pain/cramping. I began having diarrhea, during which I was overcome with nausea, was extremely hot. I was afraid I would vomit if I stayed upright, so I alternated between laying on the cool floor and waiting for the nausea to improve so I could continue having diarrhea. After my second round of alternating between the floor and the toilet, I became so incredibly hot that I felt sweat collecting on my sternum.  I had removed all of my clothing to get more skin contact with the cold floor, and reached down to feel the puddle and was able to literally dip my finger in. My stomach was cramped so much that it was extremely painful.  I alternated between diarrhea and hot flashes/nausea on the floor for some time, until eventually the pain resolved and I was able to return to bed. I was quite close to vomiting, but did not. The entirety of my time spent in the bathroom over the two episodes was ~1 hour.  The same experience happened with my first covid shot, but the entire episode was ~15 minutes. I also awoke in the night with hot flashes, severe nausea, and exquisitely painful, cramping abdominal pain, but it resolved quickly and I was fine after. The second covid shot, I had no GI symptoms but did have a flu-like reaction (malaise, fever, chills, muscle aches) that lasted ~12 hours, which I presume is unrelated to my other experiences. My last shot before this one gave me severe abdominal pain/cramping, muscle pain, and moderate overheating and nausea. The episode was ~2-3 hours overnight. The symptoms were not severe enough for me to get out of bed and move to the bathroom, as I did last night.   I never mentioned any of this before to any of my providers because I was unaware that anaphylaxis (if that is what this was) could present with GI symptoms.