Nausea and vomiting are not diseases, but rather are symptoms of many different condition, such as infection ("stomach flu"), food poisoning , motion sickness , overeating , blocked intestine , illness , concussion or brain injury , appendicitis, and migraines. Nausea and vomiting can sometimes by symptoms of more serious diseases such as heart attacks , kidney or liver disorders , central nervous system disorders , brain tumors , and some from of cancer.