Immediate (non-severe?) allergic reaction. I received the first dose of the Modern covid vaccine, injected into my left arm. I went to sit for the mandatory 15 minute "observation" period, sitting with a couple of my coworkers who were being vaccinated at this time as well. After approximately two minutes, I started feeling a little light-headed and had slight difficulty breathing. I mentioned it to my coworkers and they suggested I take off my mask (masks were required for everyone). I did so and took a couple deep breaths which made me feel better. I put my mask back on and continued chatting with my coworkers. About 5 minutes later I felt the same, slight difficulty breathing again, but thought it was probably due to my mask, so I repeated - mask off, deep breaths - and felt better. As a precaution, I stayed in the observation area for 30 minutes with one my coworkers, but did not experience any other problems. Feeling a little shaky but otherwise okay, I left at that point and walked to my car. Once in the car, I took off my mask and took more deep breaths. Feeling okay, I started my drive home (approx 7 minutes). About halfway on the drive I felt a slight difficulty in breathing again, so I rolled down the window, took deep breaths. Arriving home, I told my husband I felt "a little weird". My throat felt slightly swollen, the back of my neck felt stiff, my lips felt a bit numb, my face felt tingly and my jaw felt tight. It was about 2:45 at this point. I felt the outside of my throat with my fingers and realized my tonsils were quite swollen. My husband felt them, too, and agreed. However, nothing was visibly swollen in my face or neck, only felt inwardly. I still felt a bit shaky and had an occasional metallic taste in my mouth. I drank some water and laid down, with my feet slightly elevated. My husband stayed with me, both of us monitoring my symptoms in case anything got worse and medical attention was needed, but nothing got worse. My symptoms stayed at this level for the next few hours. I sat up occasionally and continued to drink water. I would get occasional waves of slight difficulty in breathing, but would take deep breaths and that would help. My airway never felt constricted, I just felt like I need a bit more oxygen. By early evening, I was feeling a little tired, but was able to eat dinner without problem and by about 8pm I was feeling a bit better. The swelling in my tonsils had subsided a little at this point and the waves of difficulty in breathing were getting much less often and milder. I slept through the night without problem. In the morning, however, I did not feel very well. I felt quite fatigued and had a little difficulty breathing again, but no worse than before. My arm was pretty sore from the injection, but no other symptoms had developed otherwise. By about 11am, I started feeling better, and by about 1:00pm I felt much better. I had low energy, but I otherwise felt good the rest of the day and slept fine again that night. This morning (day two) I again felt some fatigue and had a little difficulty breath at times, but by mid-morning I felt much better and have continued feeling a little low in energy, but otherwise okay so far. It is now 6:30pm on day two.