She was lost in her dreamworld all day, completely unaware of what was happening around her.

dreamworld 是由 dream（梦想）和 world（世界）组成的复合词，字面意思是"梦想的世界"，引申为"幻想世界"或"白日梦般的状态"，指一个人完全沉浸在自己想象的世界中。