You need more water.

Do you think you're hydrated? Think again. In my patients I find lack of hydration to be a common contributor to headaches, muscle tension, constipation, fatigue, poor mood and lack of appetite control. Dehydration doesn't just apply to hardcore athletes and people working in the hot sun. I see signs of dehydration in blood work all the time, and it's important that we take note. Getting in enough water, electrolytes and ABSORBING it are key to maintaining hydration.

This article from NPR's health blog "Shots" makes an excellent argument for the benefits of being perfectly hydrated. 

Here are the takeaways from this July 2018 article, called "Off Your Mental Game? You Could Be Mildly Dehydrated":

• We may be dehydrated even before we experience thirst.
• A decrease of 12% mental function occurred with 1% dehydration.
• 1% dehydration can be reached easily by sweating or not taking in enough fluids in a day.

​https://www.npr.org/sections/health-shots/2018/07/30/632480321/off-your-mental-game-you-could-be-mildly-dehydrated