Waking up with a headache can be caused by several factors, including sleep apnea, inconsistent sleep patterns (too much or too little sleep), teeth grinding (bruxism), dehydration, poor sleep posture or neck strain, hangovers, mental health issues such as stress, anxiety, or depression, and certain medications or caffeine withdrawal. Sleep disorders like insomnia and obstructive sleep apnea are common causes, as they disrupt restful sleep and can lead to morning headaches. Bruxism, where one grinds or clenches teeth during sleep, often causes tension headaches in the morning. Also, dehydration from not drinking enough water overnight or after alcohol consumption can cause headaches upon waking.

Additionally, oversleeping or poor sleep posture can cause tension and headaches. Mood disorders and chronic stress can disrupt normal sleep patterns and increase the likelihood of headaches in the morning. It is recommended to evaluate sleep quality, hydration, and lifestyle habits and consider medical advice if headaches persist or worsen.