The coronavirus disease 2019 (COVID-19) pandemic has affected millions of people around the world. Vaccination against COVID-19 has been approved for the following three vaccines in the United States: Pfizer-BioNTech, Moderna, and Janssen. Hematological complications of vaccination have been reported in the literature but remain as a rare phenomenon. We present the case of a patient who developed severe thrombocytopenia within twenty-four hours following the Pfizer-BioNTech vaccination. Commonly encountered differentials including heparin-induced thrombocytopenia and common viral etiologies were ruled out, and other causes such as drug reactions deemed unlikely as the etiology of this presentation after a broad workup. Nucleocapsid antibodies against COVID-19 were found to be positive which indicated that vaccination was at least the second encounter with this virus for our patient, which has been reported previously as the cause of immune thrombocytopenia (ITP), and this might be the culprit for sudden onset. He responded to the first-line ITP treatment with corticosteroids and intravenous immunoglobulin (IVIG) as evidenced by the fast recovery of platelet count and lack of recurrence of thrombocytopenia.