If you dream of forgetting something or someone, then this usually indicates a venting dream where you are releasing your fear of actually forgetting. Perhaps you are overwhelmed and/or the reason you are forgetting is because this is not something or someone that is very important to you, perhaps this is something you are forcing yourself to do out of obligation.
[1]If you dream that you keep forgetting, this is your unconscious mind’s way of telling you that you may have forgotten something in real life - like an important date or an appointment.
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