Nightmares are frightening or deeply upsetting dreams that usually force a person to at least partially awaken. Some possible causes include anxiety, certain medications or rapid withdrawal from them, physical conditions, traumatic events, stress, or the specific cause may be unknown. The person suffering the nightmares may be reassured but if it becomes more serious, then therapy may be required. Medication and image rehearsal therapy are also treatment options. Night terrors usually occur in children between the ages of three and twelve but they may occur in adults as well. Night terrors are characterized by intense fear and crying, difficulty waking a person, and the person having no memory of the event. Medication, psychotherapy, and awakening the person just before the night terrors usually start may all help.