Donepezil and memantine are the acetylcholinesterase inhibitors most commonly used in clinical practice for the management of mild-moderate dementia in Alzheimer's disease. Electrolyte abnormalities associated with the drugs are commonly encountered in daily clinical practice and often can lead to seizures. Hyponatremia is an uncommon adverse effects of acetylcholinesterase inhibitors. Here we present a case on hyponatremia seizure due to the syndrome of inappropriate antidiuretic hormone (SIADH) caused by the acetylcholinesterase inhibitor donepezil and memantine as other likely causes were ruled out by appropriate investigations. The causality assessment needed to be done according to Naranjo algorithm was found to be 'probable' and the level of severity according to the Hartwig scale was 'Level 5'.