No adverse event at the time of injection, except normal muscle soreness. Early in the morning of 25 December, three and a half days after the injection, at approximately 06:00 hours, just prior to the event, I had experienced some arrhythmia, which usually signals low electrolyte levels; so I took one potassium pill (Klor-Con M20, 1500 mg). immediately after taking the potassium, I began trembling and feeling weak. Suddenly, and without warning, I began shaking violently, and my blood pressure and pulse began to rise rapidly, getting faster and faster, accompanied by severe lightheadedness, as if I were about to lose consciousness. There was no chest pain. I fought the urge to pass out and managed, with difficulty, to call 911 on my mobile phone. By the time the EMTs arrived, the feeling that I was going to pass out had abated somewhat, and my thoughts were not as cloudy, but I was still shaky and weak. I managed to go outside when the ambulance arrived and walk to the ambulance that was parked at the curb. The EMTs took me into the ambulance, where they took my blood pressure (BP) and heart rate (pulse), and did an EKG. My initial BP was, I think, around 197/99, and my pulse was, if I recall correctly, around 125 (slower than it was when the episode began). The EKG was normal. By the time they took my BP, Pulse, and EKG, everything was dropping. When my pulse rate dropped to 90, and my BP had stabilized, they asked if I wanted to go to the hospital to have them examine me, and I said no. After the EMTs left, and I sat down in my home, and I began to feel better. I monitored my blood pressure and pulse. My BP steadily dropped and leveled off at 137/77, with a pulse rate of 79 bpm (beats per minute). At 07:30 hours, I took my regularly scheduled dose of Hydralazine (vasodilator). By 08:30 hours, my BP had dropped to and leveled off at 124/75, with a pulse rate of 72 bpm. My BP remained at 124/75 after the event ended. I am not sure if the event was an adverse effect of the Pfizer COVID-19 vaccine; but I think it was, because I have never had such an event happen to me before. It seems to have caused a depletion of potassium; because after the potassium began to get into my blood stream, the symptoms began to abate. By the time I took the dose of Hydralazine, the symptoms had disappeared, and I felt calm and relaxed. As I said at the beginning of this narrative, there was never any chest pain at all. It was not a heart attack or other heart event, except for the dangerously fast pulse. Today I had another attack of weakness, but my pulse did not exceed 90-95 beats per minute; and the symptoms abated a few minutes after eating two bananas and the potassium from them began to get into my system. The reason why I cannot say for sure that it is caused by the COVID-19 vaccine is because I have a tendency to not eat right at times, and I don't consume enough foods high in electrolytes to keep my electrolytes optimized. When my electrolytes get low, I am usually warned by a couple of arrhythmias, at which point I either eat foods high in electrolytes, like potato, sweet potato, or banana; or I'll take a Klor-con M20 potassium pill. Either of those solutions will begin to act within 20-30 minutes, and will raise my potassium level and stop any symptoms. I also take a magnesium supplement, plus a multivitamin with magnesium, Vitamin A, and B complex. For the two days  prior to the event, I had not eaten much, just one meal a day for the two days prior to the event. Whether the low electrolytes was brought on by the vaccine or was just the result of not consuming enough electrolytes, I am not certain. What I am certain of is that I have NEVER had such a severe episode until after I received the Pfizer booster shot.