The 3 p.m. workday slump is so rampant it’s become a cliche (you know you’re not the only one when there are memes about it), but as anyone fighting the urge to start snoozing at their desk can tell you—it’s real.

So why is this afternoon fatigue so widespread, and how the heck does anyone avoid it? According to sports medicine specialist Brad Thomas, MD, the answer is in your hydration habits.

“When you think about it, the brain is 85 percent water, so even the slightest amount of dehydration can change one’s mental performance,” Dr. Thomas says.

Read on at Well and Good