Déjà vu is the feeling of having experienced something before, even though it is the first time that you are encountering it. It can be a brief sensation or a more prolonged experience, and it may involve visual, auditory, or other sensory information. Déjà vu occurs spontaneously, and it's not something you can control or induce intentionally.

On the other hand, daydreaming is a voluntary and deliberate activity. It involves allowing your mind to wander and creating imagined scenarios or scenarios that you would like to happen. Daydreaming can be a conscious or subconscious activity, and it's often used as a means of escapism or creative inspiration.

While both experiences involve altered perceptions of reality, they differ in their causes and the degree of control that a person has over them. Déjà vu is an involuntary experience that happens spontaneously, whereas daydreaming is a voluntary and controllable activity.