Within minutes of receiving the J&J Covid shot, I felt the liquid coursing through my arm - both down towards my hand and up through my shoulder. Assuming this was normal, I sat back and planned on sitting for a few minutes as was suggested by the pharmacist who administered the shot. Almost immediately as I felt it going up and down my arm, my left hand became very tingly and I quickly started losing feeling in my fingers. At the same time, intense pressure started occurring in my throat and chest, like my throat was being squeezed and someone was standing on my chest. This made it difficult to breathe and I also noticed that my body was progressively getting hotter. Once my throat and chest felt very constricted, I leaned forward to put my head between my legs hoping to get a better breath, at which point my body felt like it was overheating. As my head was between my legs, I felt my right arm and right hand also get very tingly (like my left arm had) and couldn?t feel my fingers very well. I looked at my arms which were completely drenched in sweat - to the point that I was watching the sweat come up through my pours. At this exact moment I heard dripping and saw a puddle forming between my feet below me ? I was sweating so heavily from my face and head that it was dripping down and forming a puddle on the floor. My shirt had soaked through the chest and neck area with sweat as well. I leaned back in the chair again trying not to panic too much, but as I leaned back in the chair and focused forward on the wall in front of me, my hearing started to get very muffled - like I was in an echo chamber or something like that. It?s hard to describe other than to say it was unnatural. Almost immediately after the hearing, I felt myself beginning to black out. I?ve never really passed out like that before but something in me knew that I was going to black out and I slowly started seeing blackness fill my vision from the sides. Before Receiving the shot, I was told to go get the pharmacist ?if I had any questions? but in that moment I was not going to be able to make it around to the front of the desk area so I leaned all the way back in the chair in case I passed out and my body went limp. Luckily after a few more minutes of this, I didn?t black out and the pressure in my chest and throat had dissipated - there were knots in my stomach, though, but I?m not sure if that was from the nerves of what just happened or the vaccine. I also stopped sweating as profusely and stayed in the chair for another 15 minutes or so before hightailing it out of there. I know I should have gone to the pharmacist and told her what happened but I was just freaked out by the whole thing and wanted to go home. Based on everything I?ve read in the documentation?s I was given with the vaccine and on the CDC website, it seems like a certainty I had an allergic reaction to it - but I have no idea what I would have been allergic to in the ingredients. I?m writing this now because I?m about a week out from getting the vaccine e and though I don?t feel sick anymore (only had flu like symptoms for 2 days or so), I?m having aching sore pains in the back of my right calf / up to my lower back hamstring area. I have not worked out or exercised rigorously during the past week after getting the vaccine so my body could relax for a bit, so I?m not sure how it could be a muscle strain or something like that. I plan to go see an urgent care place within the next few days if it does not get better.