Masculine energy. If you are dreaming of snakes, look at the men in your life and ask yourself if there is an issue there with a husband, boyfriend, boss, brother, etc. Is someone in your life exhibiting low down poisonous behavior?
If you are a man then a snake may refer to your own fertility or masculine power.
A snake can also symbolize healing energy. Are you in need of emotional or physical healing? A snakebite means emotional or physical healing is about to begin. The injection of the venom is like the injection of a shot.
Snakes can also symbolize wisdom and knowledge (as in the adam and eve story). Have you learned something new recently?
May also represent a fear or temptation, something that could turn into a poisonous situation.