Vibrations like you describe can stem from a number of things.

Spontaneous OBE, or partial separation of the astral body from the physical. This is particularly likely if one has a sleep deficit, or if one is watching TV or doing a boring job, or even driving long distances. Whole body vibrations are most likely related to OBE.

You can project out of body while you are mentally awake in certain situations where, again, you are overtired or doing something boring. In essence, you will slip into an altered state of consciousness where your physical body will fall asleep, while you stay conscious and are capable of movement. In this state, you can project a low powered astral double. You will be a bit groggy when this happens.

When I feel very sad, my mind tries to escape into sleep, in order to process the events or feelings involved. This may be happening to you at times. As if you force yourself to stay awake, your physical body can fall asleep (trance state - mind awake body asleep state) and allow astral projection (and dreaming) to occur.

Vibrations can occur due to energy body growth and changes, which are causing various activations of parts of the energy body.

Energy body attachments can also cause this symptom - spirit or entity attachments.

The presence of strong spiritual fields of energy, positive and negative, can cause various activations in the energy body. For example, if I am in the presence of a person with a negative spirit attachment, particularly if I am deeply relaxed or giving contact healing, I will feel a painful nerve cramping below my right shoulder blade and the ribs there.

Robert