It's finally time to hit the sheets — except now you're suddenly in the mood to chug a few bottles of water. What gives? If you can't stop refilling the glass on your bedside table, you're not alone: it's common to feel thirsty just before falling asleep [1]. According to doctors, there are a few reasons why you're pouring another glass when all you want is some shut-eye.

Our biological clock may be one of the biggest culprits of our late-night thirst. We all have a circadian rhythm that fine-tunes the production of hormones related to the position of the sun, explained Nikola Djordjevic, MD, a general practitioner and medical advisor at Whatasleep [2]. "In the evening, we produce melatonin, which not only makes our mind sleepy, but also triggers the sleeping state of cells in which they repair and regenerate," Dr. Djordjevic told POPSUGAR. "Our body knows that hours without hydration are ahead, and it recharges our fluid supply, hence, the increased thirst at night."

But as much as biology is to blame for feeling dehydrated [3] after hours, our lifestyle choices play a role as well. The big meals we eat for dinner, like the frozen pizzas heated up an hour before bed, tend to be packed with salt. "We actually have a 'thirst centre' in our brains that make us feel thirsty when our serum sodium level increases, such as when consuming salty food," said Jesse P. Houghton, MD, FACG, senior medical director of gastroenterology at Southern Ohio Medical Centre.

The truth is, many of us aren't staying adequately hydrated [4] throughout the day, which inevitably catches up to us in the evening. And no, coffee and cocktails won't cut it. "It's good practice to drink water throughout the day, as doing so provides a wide range of benefits, such as proper detoxification, better energy and digestion, and even improved brain function," Joel Kahn, MD, FACC, a clinical professor of medicine at Wayne State University School of Medicine and scientific advisor for RDCL Superfoods [5], told POPSUGAR. "The fact is that every cell in the human body needs water to function optimally." We'll drink (a tall glass of seltzer) to that!