When kundalini is aroused, the universal life force travels up the chakra system through the sushumna.
This can be like a snake winding it's way up the spinal cord. If it is not balanced by an equal force (snake) winding up in the other direction, the experience can be very painful and feel like one is on fire - burning up.
If one is not ready, the awakening can be very traumatic.
Can also be a metaphor for the awakening of thinking in humans as the "snake" in the garden that traveled up The Tree of Life towards Binah, Kether and Chokhmah. In order to prevent this, Malkhuth was poked out and fell to the foot.