People with schizophrenia often have delusions or hallucinations. A schizophrenic delusion is a belief that is very different from what other people with the same way of life believe. Hallucinations are usually experiences of hearing voices that don't exist. These voices often say unpleasant things to the person. Many people can hear voices like this without being schizophrenic, for instance right before falling asleep. This is called a hypnagogic hallucination. The brain cannot tell them apart from normal sounds that are heard. This is not yet fully understood by science.