Perder algo
Algo que tenías se ha ido — a veces el sueño te pregunta qué.
Losing something in a dream is the dictionary's image of recognising an absence. The dream is often more useful than waking life is at noticing what you have actually lost. On waking, the question to ask is not just 'what was the thing in the dream' but 'what in my life feels like that thing'.
Where you often see it. Searching pockets and finding nothing. Losing a wallet you cannot describe. The dream uses losing for something you had has gone — sometimes the dream is asking what.
What it is not. A losing dream is not always a literal anxiety. The dictionary reads it as the dream pointing at the question of what mattered.
Related in the dictionary. Read losing with searching (its partner), key, money, and any scene of inventory.