The most prevalent cause of flaccid paralysis was Guillain-Barré syndrome, with several clinical variations. Although autonomic dysfunction was commonly observed in the clinical course, it was generally neglected in the pediatric population and was rarely the first presenting symptom. Researchers discussed the case of a previously healthy 17-year-old who presented to the Emergency Department with lipothymia-related gastrointestinal symptoms. An initial electrocardiogram (ECG) demonstrated prolonged sinus bradycardia subsequently connected with arterial hypertension. Structural and inflammatory heart pathology was ruled out, and auriculoventricular conduction block and posterior reversible encephalopathy syndrome. The patient displayed sensory and motor nerve abnormalities on the ninth day following the onset of symptoms, with a distinct albumin-cytologic separation in the cerebrospinal fluid, consistent with an unusual presentation of GBS with autonomic dysfunction. After receiving immunoglobulin therapy, the patient developed aseptic meningitis, necessitating the termination of previous medication and treatment with plasmapheresis. With full motor function recovery, clinical improvement was achieved. This case shows a Guillain-Barré syndrome variant in which autonomic dysfunction occurs before neurologic deficiency, which was unusual in children, underscoring the importance of considering this as a differential diagnosis for severe bradycardia in children.