Dehydration is something that can really sneak up on you, especially if you’re not aware of what you’ve been drinking and the type of activity you’re participating in. Here are some simple warning signs of dehydration and how you can best prevent these symptoms before they happen.

1. Dizziness and confusion.

Feeling “woozy,” dizzy, or confused while running can be a sign that your blood pressure has dropped due to dehydration. Since your blood is mostly made up of water, when you dehydrate, the effects can go right to your head—literally.

2. Dark-colored urine.

Keep an eye on both the frequency and the color of your urine. If you haven’t peed in the last two hours, it’s likely that you haven’t been drinking enough water. Additionally, if your urine is dark (i.e., the color of apple juice) rather than pale (like lemonade), you’re dehydrated.

3. Dry mouth and dry skin.

A dry, sticky mouth is a sign that you haven’t been drinking enough. Drink regularly throughout the day to avoid this feeling. Also, if your skin is dry or has lost some elasticity, it may be a sign that fluid levels in your body are low.

4. Heavy sweating.

Sweating while running is an essential way for your body to cool itself. The downside, however, is that it results in fluid loss. Be careful to replace fluids lost through sweat by drinking water and sports drinks during longer runs and on warmer days.

5. Headache.

When your body has a hard time maintaining adequate fluid levels, it has a hard time supplying adequate levels of blood and oxygen to the brain, oftentimes resulting in a headache. If you feel a headache settling in, reach for a glass of water or a sports drink to elevate hydration levels.