Why do we get nightmares?

Nightmares usually occur during rapid eye movement (REM) sleep, the stage when the brain is highly active and most vivid dreaming takes place, typically in the second half of the night. While the exact purpose of dreaming is still debated, many scientists think dreams help the brain process emotions and memories, and nightmares may reflect the mind working through fear, stress, or unresolved experiences. Common triggers include anxiety, traumatic events, fever, certain medications, and irregular sleep schedules. For most people nightmares are occasional and harmless, but frequent, distressing nightmares can be a feature of conditions like post-traumatic stress disorder. Good sleep habits and reducing stress often lower how often they occur.