Physical urges and emotional energies that have not yet been developed and are in need of differentiation. It could also mean encountering the massive and devouring energies of the unconscious, particularly physical urges and emotions.
The devouring mother or woman; the devouring unconscious, animalistic but also comic.
According to Jung, the monster, the evil, that wants to swallow you up.... Little Giant Encyclopedia
A mammal living in water and on land signifies the mediation between the elements of water, your emotions, the earth and your body. It may comment on a big emotional issue that has affected your health. With its huge body, a hippopotamus often comes to represent the undertaking of a big project in which you may have some mud to wade through before you can complete it.... Ariadne's Book of Dream
Depth Psychology: Seeing a hippopotamus: while you present to the world a picture of authority (in behavior and appearance), deep down you feel that you are standing on “wobbly” legs. See Animals, Whale.... Dreamers Dictionary
Dreams of a hippopotamus are showing you that you have a wonderful balance between your masculine energy that can be dominating and intimidating and your feminine energy that can flow with the stream of life.... Strangest Dream Explanations