Sleep is when the brain consolidates what you've learned that day into long-term memory. Sacrificing sleep to cram for extra hours is close to self-defeating — studies consistently show students who sleep normally before an exam outperform those who pulled an all-nighter, even when the all-nighter group studied more total material.
Exam-period stress also commonly causes racing-thoughts insomnia — lying awake running through material or worst-case scenarios. A worry dump (writing down what's spinning) before bed, or a fixed 'worry time' earlier in the evening, genuinely reduces this.
Caffeine used to power through late study sessions has the same delayed-effect problem as any other time — a coffee at 9pm to keep studying is still active in your system well past midnight.
If exams are approaching, protecting a consistent sleep schedule in the final week matters more than an extra few hours of last-minute revision — your brain needs the sleep to actually retain what you've already studied.
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