Robert Bruce teachings agree with what I was taught. Here's a quote from "Treatise on Astral Projection, Part 5" by Robert Brucehttp://www.astraldynamics.com/tutorials/?BoardID=65&BulletinID=271http://www.astraldynamics.com/tutorials/?BoardID=65
The vibrations are an effect and NOT a cause of projection. When enough pressure is exerted on the astral body to loosen it sufficiently, the energy body expands and energy flows through the chakra system to be stored in the energy body. This flow of energy through the hundreds of chakras and their connecting web, or meridians, CAUSES these vibrations. This normally happens, unnoticed, during sleep.
I've found there are a lot of parameters such as how tightly bound your astral is to the physical. If it's tightly bound then it will take a great deal of energy to break it free. This energy is flow of chakra energy, which is usually sensed as vibrations. In this case the vibrations will be intense. I've felt the vibrations so strong that it literally felt like my entire physical body was shaking, mostly my head. Although this is not the physical body shaking. As people become more adept at projecting then the bond between astral and physical bodies is loosened. Also, a lot of people are just born with a loser fit. In this case, it will not take much energy to project. So the person may not even feel any vibrations.
When you meditate you'll probably eventually learn that there's something that expands away from your material body. You'll learn to willfully expand this energy body. When this happens it will feel like someone's sticking you with tiny pins. This is just your higher bodies expanding. When they appreciably expand then you should begin to notice your body becoming numb. The more it expands the more numb you feel.
Lowering your heart rate can significantly lower the amount of energy required to release the astral and partial Etheric. Energizing the 3rd eye chakra greatly increases your energy flow, which when really energized will usually last for hours.
People raising their kundalini may often feel vibrations.
As everyone says to protect against law suites, Please make sure you consult your doctor before doing anything.
Of course, if you just want to have a good old lucid dream (not really leaving your body) then you can ignore all the above.
This is all just the tip of the iceberg.