SEIZURE; SLURRED SPEECH; LEG PAIN; HEADACHE; SORE ARM; FEEL WEIRD (NOT HERSELF); This spontaneous report received from a patient concerned a 59 year old white and not Hispanic or Latino female. The patient's height, and weight were not reported. The patient's concurrent conditions included hypothyroid. The patient did not do drugs. The patient received covid-19 vaccine ad26.cov2.s (suspension for injection, route of admin not reported, batch number: 1808609, expiry: 09-JUN-2021) dose was not reported, 1 total, administered on 20-MAR-2021 to right arm for prophylactic vaccination. No concomitant medications were reported.  On 21-MAR-2021, the patient experienced sore arm the next day after receiving vaccine. On 22-MAR-2021, The patient had headache the following week that did not go away for about 5-7 days and nothing was relieving the pain. On 24-MAR-2021, the patient experienced leg pain and thought it was arthritis but she had never had leg pain like that before and her legs were really hurting. On 04-APR-2021,Sunday the patient was still feeling it. The next day woke up fine but still had leg pain and decided to take a hot bath and she really started to feel weird (not herself) and she was talking to the delivery woman and she was slurring her words (she did not do drugs) and was a healthy person. The patient laid down and her fiancé wanted to take her to the hospital. The patient's mom came over and she wanted to show her a new fridge and called it a fire place. 911 were called and the patient was taken to the hospital and admitted with seizure for 5 days. The patient had the seizure 15 days after the JnJ vaccine on 05-APR-2021, in the afternoon. The patient underwent 2 Magnetic resonance imaging (MRI) and a bunch of tests, computed tomography scan (CAT scan), electroencephalogram (EEG). No MD could claim this was from the JnJ vaccine. It was reported that the patient never had a seizure before in her life. A colleague told the patient that she read an article that said that she could have seizures and she was hypothyroid and thought that it a contraindication to the vaccine. The patient was admitted for 5 days and all tests came back normal. The patient was having speech issues but they were improving. The patient's mobility was fine and eye function was fine. The patient missed a lot of work. The patient had follow up with neuro in a month and would see another neuro and pen medicine and it was an ongoing situation. This was to make sure that everything was okay. Laboratory data (dates unspecified) included: CAT scan (NR: not provided) Normal, EEG (NR: not provided) Normal, and MRI (NR: not provided) Normal. The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The patient recovered from seizure, leg pain, and headache on 2021, and sore arm, was recovering from slurred speech, and the outcome of feel weird (not herself) was not reported. This report was serious (Hospitalization Caused/Prolonged).; Sender's Comments: V0-20210552079-covid-19 vaccine ad26.cov2.s -Seizure- This event is considered un-assessable. The event has a compatible/suggestive temporal relationship, is unlabeled, and has unknown scientific plausibility. There is no information on any other factors potentially associated with the event.