Injury

• One common cause of nausea and headache is a blow to the head, or a concussion. One problem with concussions is that sometimes the person feels fine after the blow and immediately goes about normal activities. The headache and nausea may come minutes later or a day later. If you are experiencing headache and nausea, visual disturbances, dizziness, impaired balance, prolonged memory loss, ringing in the ears or the loss of smell or taste after an injury to the head, seek medical attention. The American Academy of Pediatrics suggests that any child who has received more than a slight bump to the head should be seen by a pediatrician.
  
  

Neurological Conditions

• The Michigan Headache and Neurological Institute lists several neurological conditions that can bring about nausea and headache. These can be from unknown reasons (such as migraines and cyclic vomiting syndrome), from problems of balance or the inner ear (such as tinnitus, vertigo, motion sickness and Meniere's disease) or from a genetic condition (such as Arnold-Chiari malformation). Headaches can also be due to a problem that doesn't actually originate in the head, but the pain is perceived to be coming from the head. An example of this is cerviogenic headache, where the nerve in the spine reaches up to the head and so a person feels pain in the head.
  
  

Chemical-Induced Headache & Nausea

• The body is controlled by chemicals. When a new chemical is introduced--or taken away--the body feels as if it is no longer in a state of normalcy. It uses the device of pain--usually in the form of headache and nausea--to get the person to either purge the new chemical from the body or to imbibe the missing chemical. Chemical causes of headache and nausea can be from hangovers, withdrawal (even from legal prescription medications, nicotine or caffeine) or from taking a new medication.
  
  

Infection

• Another common cause for headache and nausea is that the body is suffering from a bacterial, viral, parasitic or fungal infection. This usually causes a fever, which in turn causes headache, nausea and other symptoms such as muscle cramping, diarrhea and sore throat.
  
  

Warning Signs

• According to the Mayo Clinic, a sudden headache that increases in pain over time and brings on nausea could be the sign of a ruptured brain aneurysm. This needs immediate emergency care. Also, the common symptoms of a stroke are sudden headache, nausea as well as confusion, numbness on one side or in a limb and a visible drooping of one side of the face. This also needs immediate medical attention.