What are these sensations I sometimes feel during sessions?
I've been meditating with a diligence I never had before for about a month now and sometimes I feel this sensation that is something between a tingling and a "vibration", almost always this happens on the extremities of the body, either on my feet or hands, it's a very relaxing and pleasant feeling. As long as I don't move my body and just observe it, it'll continue for varying times that depends on the day and the session. Thanks
That's a result of meditating correctly - i.e. mind is calm, pacified, body is pacified. The moment one does that, a force/pressure pervades everywhere in the body, increasing the force of circulation of blood, lymph, and other qi and non-visible energy is magnified. Most people will feel it more prominently in the extremities: hands, feet, skin. Because what you feel is the contrast between normal agitated mind, and the mind in samadhi where circulation of energy is amplified greatly.
With practice you can turn on samadhi like a switch, on demand, anytime, any posture. You could be standing in the line at the grocery store, going into a relaxed meditative state, and feel the pleasant buzzing vibrations, heat, electrical sensations, goose bumps, endorphins, etc.