Nightmares

I was getting used to them.
But, today I was swimming with dolphins. They were saving me from the snake. I barely got away in the end.
The would let me touch them. One of them had wounds all over him - I was scared to touch him, but it sort of mirrored at me.

The meaning of dolphins in your dreams:
Dolphins represent friendliness, communal living, rescue, communication, and affection. They are water dwelling mammals and in our dreams they represent our willingness and ability to navigate through emotions. They represent positive messages from our unconscious minds. Dolphins could also represent a positive connection between our consciousness and to those parts of the psyche that is a mystery and largely unconscious.

Snake
Each dreamer must consider their own situation and all of the details of the dream. Sometimes snakes may be phallic symbols and other times they represent negativity in our lives that hampers our progress and constantly threatens us. In the long run the snake may be a positive symbol; it may represent difficulties that lead us to the center of personality and result in feelings of completeness.

This is amazing. How, and who comes up with these definitions and meanings?