This is most likely anticipatory sleep difficulty (fear or anxiety about not being able to sleep), where the brain becomes mildly alert before an important event, even if you do not feel stressed. It is a common conditioned response that can temporarily disrupt normal sleep on exam nights. Taking a sleeping pill for a single night is generally not recommended without medical advice, as it may cause morning drowsiness and affect concentration during the exam. It is better to use relaxation techniques, avoid caffeine in the evening, and follow a consistent bedtime routine before exams. Please seek medical advice if the problem persists.