External stimuli invade our dreams

This is called Dream Incorporation and it is the experience that most of us have a real-world sound heard in our dream and incorporated in some way. A similar example occurs when you feel thirst or urination during sleep in the real world and this is transported to the dream. Most children, already large, bedwetting because of incorporation: are with a full bladder, dreams that are tight and urinate in the dream while you wet the bed. Thirsty people during sleep reported taking glasses of water inside the dream, minutes later, get thirsty and have another glass. The cycle repeats until the moment that this person wakes up.

The famous Salvador Dali painting above explains exactly this concept. His name is "Dream Caused by the Flight of a Bee around a Pomegranate a Second Before Awakening".