Hearing voices in the head is not always a sign of mental illness, according to Psychology Today. Traumatic events such as physical or sexual abuse, the loss of a loved one or an accident may trigger auditory hallucinations.
Hearing voices may be associated with fevers, substance abuse or withdrawal, says Healthgrades. Sleep deprivation or severe fatigue may also cause these auditory hallucinations. Hearing voices may accompany or precede migraines, according to PubMed. The onset of tinnitus may also cause phantom sounds such as voices, states The American Academy of Audiology. However, when voices, speech and complete sentences are heard without actual conversation taking place, it may indicate a mental illness that requires attention.