Dreams and visions about a hippo tell you about strength, inner power, but also talent and possibilities to adapt. Another explanation is that you project personal experiences and traits onto the hippo.
You can think of coming across as being slow and unwieldy, but being unexpectedly aggressive. Dreams or visions of a hippo attacking you tell you about inner anger and fear, losing something you could rely on. An important explanation is that you project your own behavior, fears, anger onto the hippo, so you attack yourself.
Another explanation is that a hippo evokes the holiday feeling. You can also think of a different climate or country, culture and the desire to go to or work on this in your waking existence. Clearing old unhealthy emotions and feelings and letting go of pent-up experiences by, as it were, leaving it behind.