If you see a jellyfish in a dream, then such dream foretells about your negative past. Perhaps there are some hidden anger you were unable to express, therefore you are dreaming about it. There is also a possibility that you feel some kind of anger towards particular person in your waking life. On the other hand, the dream indicates the lack of self-trust you are suffering from.
Read more about dreaming of Jellyfish in other dream meanings interpretations.