Diving may be a sexual symbol, representing male penetration. Water often symbolizes the feminine.
(Deep) water sometimes symbolizes the unconscious; so diving may symbolize descent into the unconscious. If this is the case, it will usually be a sign that your dream is recommending you to get in touch with your unconscious. Perhaps there are unconscious motivations - desires or fears -that are causing you to function inefficiently; some neglected or undervalued part of you that you need to learn to respect and utilize if you are to achieve (fuller) satisfaction or happiness.
There are myths of divers who plunge to the depths of the sea and bring up treasure. In psychological terms this represents either what is described in 2 above.
The Diver dream may be a visual representation of the link between the Unconscious and conscious mind. A diver retains air by holding his or her breath, or by utilizing the proper scuba equipment, or other breathing apparatus. The air in this sense embodies the surface, or conscious world, which ‘remains’ with us, even though submerged in the dark, mysterious and enigmatic Unconscious. As such, the diver dream may illustrate a dreamer searching for a ‘rational’ solution to a riddle which is out of his day to day experience, or understanding. Moreover, if in the dream, the diver faces difficulties or danger, all the threatening factors and forces therein, (shark, whale, whirlpool etc.,) should be analyzed for their full waking ramifications. If the diver is in control of his dive, the dreamer may be experiencing control over his or her emotions. In this sense, the dreamer is balancing his psychological and emotional foundation.