Dreams are a series of thoughts, images, and sensations that occur during sleep, primarily during the REM sleep stage. They can be influenced by daily experiences, emotions, and memories, often reflecting a person's subconscious mind. Dreams can vary in content, ranging from mundane scenarios to fantastical adventures. Nightmares are distressing or frightening dreams that can cause feelings of fear, anxiety, or sadness upon waking. They often involve themes of danger, loss, or personal conflict. Nightmares can be triggered by stress, trauma, or certain medications, and may disrupt sleep, leading to fatigue and emotional distress.