You are sourced from pure positive energy and when you tap into this energy through your focus, you experience positive emotion, but when you disconnect from this source of energy, you experience negative emotion instead.
Thus, positive emotion is your allowing of the energy to flow through you while negative emotion is your blocking of the energy from flowing through you. Positive emotion is indicative of an increasingly energized state while negative emotion is indicative of a decreasingly energized state.
For this reason, when you choose to align with pure positive energy, you feel good, but when you choose not to align with this energy, you do not feel so good due to the differences in energy levels you experience, for high energy levels feel very good to experience compared to lower ones. Also, the better a point of focus feels to you, the more you are allowing pure positive energy to flow through you.