Headaches can occur for several reasons, such as mental fatigue, dehydration, muscle tension, eye strain or sessions that are more intense than usual. It may take some time to get used to the electrodes on your scalp and this may cause temporary headache. Ensure the headset is snug but not too tight. Ensure you are well hydrated, comfortable, and not overtightening the headset. If headaches continue or worsen, consult a healthcare professional.