Background: Epilepsy is defined as permanent tendency of the brain to generate epileptic seizures. Differentiation between psychogenic non-epileptic seizures (PNES) and generalized convulsive epileptic seizures (ES) is important for therapeutic decision making in the emergency department (ED). Up to one fifth of patients who present with seizures do not have epilepsy. The majority suffer from psychologically mediated episodes; dissociative seizures, often referred to as ‘‘non-epileptic seizures’’. Most patients are falsely treated for epilepsy for several years with more antiepileptic drugs (AEDs) at higher doses and with more side effects. Anion gap (AG) is the difference in concentration between unmeasured anions and unmeasured cations. We can estimate the value of anion gap according to the following equation: Anion gap= Na+ - (HCO3 - + Cl- ). Clinician uses anion gap to classify acid–base disorders. Tonic‐clonic seizures (TCS) either generalized onset (GTCS) and focal to bilateral tonic‐clonic seizures (FBTCS), are commonly associated with strong and sustained convulsions of a large number of body muscles along with respiratory arrest and tachycardia, leading to considerable metabolic stress which can be assessed by anion gap. Methods: The study was conducted through comparing results of anion gap analysis between 2 groups of patients who present with generalized shaking attacks according to non-medical witnesses. The study included 60 patients, recruited from ER in Benha university hospitals in 2021, divided in 2 groups, each is 30 patients. One group had true ES and the other group had PNES according to a neurologist observer. Results: There was a significant difference between anion gap values of different groups. ES: 17.79 ± 5.49 range (6.6 - 35) and PNES: 13.45 ± 2.85 range (7.6 – 18.7), p