Your sleep style itself can influence your dehydration overnight, according to the National Sleep Foundation. "Even if you start the night reasonably well-hydrated, you’ll lose some body fluids simply by breathing while you sleep," they note. Though, some methods of breathing are more prone to causing dehydration than others. "This is especially true if you breathe through your mouth, snore, or have sleep apnea. If you breathe through your nose while you slumber, you won’t lose nearly as much water from your body," says the Foundation.

Sweating in your sleep can be caused by simple overheating or other conditions, including infections, but either way, if you wake up in a pool of sweat in the middle of the night, you're much more likely to feel dehydrated the next day. Night sweats are repeated episodes of extreme perspiration that could soak your pajamas or bed. Treatment of the dehydration needs to target the cause of the sweats themselves, which your doctor can help you suss out.

While you might like to bake like a loaf in an oven overnight, it's likely to lead to dehydration in the morning. "An overly dry or warm bedroom can also lead to extra fluid loss during the night," says the National Sleep Foundation. Perspiration can mean you wake up parched. Science also indicates that a cooler temperature in bedrooms is better for restful sleep, and sleeping with a humidifier on can help combat dry winter air.

When you're at a part of your menstrual cycle where estrogen dips, you're more likely to be dehydrated, including during your sleeping hours. This is because estrogen is related to the body's ability to retain moisture, and when it dips — both in your regular menstrual cycle and in menopause — your risk of dehydration rises. "Estrogen and progesterone influence your body's hydration levels, and when the two are roller-coastering, like when you're in the throes of PMS, you may need to increase your fluid intake to stay hydrated,” says Health magazine.

Another possible culprit for dehydration when you wake up? "A late-day intense exercise session without sufficient rehydration," says the National Sleep Foundation. The problems with late-night exercise go beyond hydration; it can also disrupt your internal clock and sleep cycle, making you tired the next day. Try exercising at the same (slightly earlier) time each day, and making certain to refuel on water after.

Several categories of medication increase the risk of dehydration at night, including anti-depressants. Dr. Amy Esposito, M.D., told Self that decongestants are particularly prone to causing dry mouth in the morning: “It’s intended to fix nasal congestion, but the medicine can’t just target nasal vessels, so it just makes everything dry.” Talk to your doctor about whether medications you're taking can increase dehydration.