Why do dreams feel so real sometimes?

Dreams can feel so real because, during REM sleep and sometimes other sleep stages, your brain is actively generating a vivid internal experience while the usual awake-state checks on reality are weakened.

A few things contribute:

• Sensory areas are active: Brain regions involved in visual and other sensory processing can become active during dreaming, which helps create detailed scenes, faces, sounds, and movement.
• Emotion is strong: Emotion-related networks, especially the amygdala, are often active, so dreams can feel intense, frightening, joyful, or deeply meaningful.
• Reality monitoring is reduced: Parts of the prefrontal cortex involved in logic, self-monitoring, and questioning whether something makes sense are less active, so odd events can seem normal while you are dreaming.
• You are immersed in the experience: During a dream, your mind is usually fully engaged in the dream world, so it can feel convincing until you wake up.

As for the body, during REM sleep the brain sends signals that inhibit most voluntary movement, which is why you usually do not act out your dreams.

In short, dreams feel real because your brain is building a rich, emotionally charged simulation with less of the usual waking reality-checking turned on.