FAST HEART RATE; BLOOD CLOT IN BOTH LUNGS; ACHY; LOW ENERGY; VERY WEAK; HEADACHE; FEVER; This spontaneous report received from a patient concerned a 72 year old female. The patient's height, and weight were not reported. The patient's concurrent conditions included fibromyalgia. The patient received covid-19 vaccine ad26.cov2.s (suspension for injection, route of admin not reported, batch number: 1805022, and expiry: UNKNOWN) dose was not reported, administered on left arm on 13-MAR-2021 for prophylactic vaccination. Concomitant medications included pregabalin(Lyrica) for fibromyalgia and bad back. The patient reported pregabalin makes her gait off. On 13-MAR-2021, the patient felt okay. On 14-MAR-2021, the patient experienced  achy, low energy, very weak, headache, fever of 100 degrees fahrenheit. Laboratory data included: Body temperature (NR: not provided) 100 F. On 13-APR-2021, she had wellness visit. The patient had a fast heart rate. Laboratory data included: Heart rate (NR: not provided) 144 (units unspecified). So immediately her electrocardiogram was taken and she was hospitalized for 2 days in emergency room by ambulance and started running tests. The patient had a computer tomography with dye contrast and it showed blood clots in both lungs. She had many tests, echocardiogram and X-rays. Treatment medications (dates unspecified) included: continuous oxygen via nasal prong (3.2 litre down to 2 litre), warfarin sodium(Coumadin), blood, whole, and rivaroxaban(Xarelto). The patient stated once she had rivaroxaban she felt "free". Currently also had 2 intravenous and taking blood regular.  She was also on physical therapy. The therapist came in and made her walk across her room twice according to therapist she did not need oxygen. The patient currently had 2 IV's and taking blood regular. The patient will be discharged with or without the oxygen. The patient has machine on her chest with all kinds of wires. She don't know about her oxygen saturation. The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The patient recovered from achy, low energy, very weak, headache, and fever on 15-MAR-2021, had not recovered from fast heart rate, and the outcome of blood clot in both lungs was not reported. This report was serious (Hospitalization Caused / Prolonged and Life Threatening).; Sender's Comments: V0: This is a 72 year old female, unspecified ethnicity, who experienced tachycardia and was noted to have blood clots in both lungs 32 days (around 1 month)  after receiving the COVID-19 vaccine ad26.cov2.s on the left arm. Patient  had Fibromyalgia and is maintained on Pregabalin (Lyrica). Patient's height and weight were not reported as well as history of smoking, allergies or drug abuse. One day after receiving the vaccine, the patient experienced fever, headache, weakness and pain, which resolved. During a wellness visit after a month from the vaccine, tachycardia was noted and an EKG was done. Patient was immediately brought to the ER, where the CT Scan (with contrast) showed blood clots in both lungs (detailed result not reported). Other tests done were also not reported. Patient was subsequently admitted in the hospital and was discharged after 2 days. The information provided is insufficient to show that the vaccine is causing the event; hence, this is assessed as indeterminate per WHO causality classification of adverse event following immunization. Additional information requested.