There are several possible connections between severe headaches and nausea. Sometimes the headache itself is causing the nausea, especially in the case of migraines. In other cases, they can be two separate symptoms of a common disorder or condition. A lot of viruses and other illnesses that affect the stomach can also cause headaches, and this is one of the main connections.
When most people describe severe headache and nausea in direct association with each other, they are talking about migraines, and there is some research into how that connection works. Migraines are generally caused by a swelling in the blood vessels inside the brain, and this sort of swelling seems to be related to serotonin levels. There is also research suggesting that lowered serotonin levels can make people feel nauseous. Not all people who have migraines suffer with nausea, but it is very common. Sometimes migraine-related nausea is triggered by motion, and sometimes it doesn’t have any direct cause other than the migraine itself.
Another common condition where severe headaches and nausea can co-exist is a hangover. Many people who use alcohol may experience a very unpleasant condition as the alcohol wears off. This is usually felt the next morning after waking up. It has some symptoms in common with migraines, including sensitivity to light and sound, along with severe headaches and nausea.
There are many viruses and bacterial infections that cause severe headaches and nausea at the same time. Influenza, for example, is well-known to cause both symptoms. This is partly because both symptoms are manifestations of the immune system fighting off an illness. When a person becomes infected, one of the reactions of the immune system is often a fever, and fevers can potentially cause a headache. Another way the body has of dealing with foreign invaders is to expel things through vomiting and diarrhea, so a person may also become nauseous.
People who experience severe headache and nausea usually treat each condition separately. Most medicines that help control headache pain are not especially beneficial for nausea problems and vice-versa. Sometimes it is possible to focus treatment on the underlying condition, and if this approach is successful, the symptoms will generally go away as well. Some common drugs that help with headache pain are non-steroidal anti inflammatory drugs (NSAIDs), acetaminophen, and special prescription medications. Treatments for nausea vary significantly depending on the underlying cause of the condition, but they could include things like promethazine hydrochloride.