Sometimes in and out of meditation I feel a brief vibration usually lasting 5-10 seconds and usually to the right or left of the base of my spine. What is this?
—susan fritz, us
It is not uncommon, especially if you meditate regularly, to feel vibrations, or other such feelings, in or around your spine.
This generally means that you are beginning to awaken the kundalini power locked in the base of your energy spine near the first chakra.
This is nothing to be alarmed about. In fact it is a good sign that your meditations are being effective.
If you want to study up more on what kundalini is, how it works, and how to work with it safely, one excellent place to start is The Art and Science of Raja Yoga. It is presently out of stock, but it should be available again in February.