There are many different factors that can cause headache and nausea to occur together. Some common causes include:

• Migraines: Migraines are a type of headache that can cause severe pain, light sensitivity, and nausea.
• Food poisoning: Consuming contaminated food can cause headache, nausea, and other symptoms.
• Motion sickness: Motion sickness can cause headache and nausea, especially when traveling by boat, plane, or car.
• Concussion or brain injury: Head injuries can cause headache and nausea, along with other symptoms.
• Viral infections: Some viral infections, such as the flu, can cause headache and nausea.
• Dehydration: Dehydration can cause headache and nausea, along with other symptoms.

It's important to seek medical attention if the headache and nausea symptoms persist or become severe. A healthcare provider can diagnose the underlying cause of the symptoms and recommend the most effective treatment options. Monitoring these symptoms regularly can help prevent further health problems and ensure a quick recovery.