Kundalini is latent energy. When you do meditation, latent energies rise up. Meditation pulls inside energies up. This whole process is called 'Awakening of Kundalini'. In the process of Kundalini, different things happen to different people depending on their past lives, the intensity of practice of meditation in the current life.. and many, many other factors.
When you begin the practice of meditation, first the hard and harsh things come out based on the past karmas one had done. But one must cross that phase. Once the bad negative karma coming from the past lifetimes is burnt, then beautiful things will begin to happen. These experiences are called as Kundalini Experiences.