What Actually Happens to Your Brain When You Don’t Sleep Enough

I’ve always wondered what exactly happens inside my brain after a sleepless night. Why does everything feel harder—thinking through problems, remembering where I put my keys, even just reacting quickly enough to catch something before it falls? We tend to describe it vaguely: “I’m exhausted,” “My brain isn’t working,” “I can’t focus.” But what does that actually mean on a biological level?