Pt. requested and received the J&J / Jansen COVID 19 vaccination yesterday at 1317.  While he was being monitored for any adverse reactions, Pt. asked if lightheadedness was a side effect of the shot.  Writer advised that it could be and that everyone is different.  Writer asked if he would like some water, and he declined. Pt. was advised to remove his mask so he could breathe better.  Writer took his pulse while I gathered information.  It was 96.  Pt. reported that he did eat lunch, is drinking plenty of water and fluids.  He relayed he is keeping food down and not having any other issues. Pt. is currently on opiate withdrawal protocol.  Writer asked about his breathing and his chest.  Pt. relayed he was not having difficulty breathing and denied any chest pain at all.  Writer spoke with the Deputy to be sure that we kept an eye on him for a bit longer after his 15 minutes while he was in his cell, due to his lightheadedness.  Pt. was talking with writer, answering questions with ease.  Pt. was not diaphoretic and did have good color.  His pulse was checked again, and it was 84. At 1333, when his 15-minute observation was done, writer went to assist pt. to his feet and informed him that I would escort him back to his cell because he was still feeling a bit uneasy.  When he stood, pt.'s knees buckled, and he knelt to the ground.  Writer helped pt. to lay down.  It was a smooth transition, and he had no injuries to his head or body.  Pt. had what appeared to be a short spell where his body completely tensed for a few seconds, then he relaxed.  He was having a hard time keeping his eyes open, but when prompted, was able to open his eyes.  The Deputy standing by was asked to call for the Public Health Nurses, who had moved on to the next POD to continue vaccinating.  Once on the scene, pt.'s blood pressure was obtained.  142/80.  His pulse was 82.  During this time, it appeared that the tensing episodes became more frequent and a bit more severe.  They were happening approximately every 30 seconds, and lasting between 5 and 10 seconds.  EMS was activated at approximately 1340.  Pt. was awake during these episodes, and communicated with the nurses attending to him. While attending to pt. and waiting for EMS, it was at that time that pt. admitted that this was not the first time this had happened.  He admitted that about a week ago, the same thing happened.  When that new information was explored, pt. reported that his wife thought he had "Serotonin Syndrome".  Writer asked what meds he was taking on the outside and he reported that he only takes methadone form the clinic.  He denied any other medications or street drug usage.  He does not take any mental health medications at our facility. Collectively, the nurses that attended to him after this episode agreed that this is an isolated incident and not related to receiving the COVID vaccine.  EMS arrived at approximately 1347, and report was given.  He was transported to the hospital for evaluation. Pt. was returned from the hospital at approximately 1600.  The Officer that accompanied him reported to facility that the hospital also believed this was an isolated incident, most likely related to withdrawals.  They did not believe that receiving the vaccine was a factor in today's events.  Labs were drawn at the hospital, and were all WNL.   Once back in custody, writer spoke briefly with pt..  He was feeling much better, and was sent back to his cell without further incident.