Dreams that occur early on in the night tend to deal with pressing issues or something on your mind. The feeling in the dream is often the key to understanding it. Since you woke up feeling tense and scared, this probably has to do with a situation in your current life that you do not want to face or are afraid to face. Since it it involves a snake, it is probably energy related. There are three things that should help you understand this better and that is the black and yellow coloring of the snake (probably having to do with the naval/solar plexus chakra and the unknown; the fact that you were scared and holding it in your left hand, which typically has to do with receiving.