To dream of a cactus is an indication that you feel your personal space is being invaded. You feel unable to breathe and are seeking space and privacy. The spines of the cactus are the physical representation of this wish. In many cases, you may feel you are in a situation you cannot get out of. Conversely, the cactus may indicate a personal desire to learn to protect yourself.
To dream of a cactus may also be a subconscious reminder that you need to learn to grow as your life changes.