Feeling out of sorts and don’t know why? You might be dehydrated. Two new studies found even mild dehydration comes with big consequences: altered mood, impaired memory, trouble concentrating, fatigue, headaches and anxiety. While the reasons for these symptoms are unclear, researchers at the UCONN Human Performance Laboratory noted that dehydration causes changes in electrolyte balances in the blood as well as serotonin levels in the brain, which can affect memory and mood.