Feeling of being sick closely associated with vomiting, often preceding or accompanying it; sometimes vomiting relieves nausea completely, or reduces the feeling. Causes, as with vomiting, are stimulus of the stomach wall or the vomiting centre in the medulla oblongata of the brain. Some brain conditions, particularly tumours and high pressure in the brain, which sometimes cause vomiting, are not unnaturally also associated with nausea. Well-known and frequent causes are motion sickness (including carsickness and seasickness), overeating, and excessive consumption of alcohol. Nausea is also often felt in the first months of pregnancy, particularly in the morning (morning sickness); this is caused by hormonal changes that occur in pregnancy. In most cases a doctor need not be consulted in the event of nausea, unless it is severe and associated with vomiting, in which case examination and treatment may be necessary. Nausea itself is a harmless symptom.