I would like to add that meditation is not just an overwhelmingly positive experience. Meditation will frequently dig up old thoughts and feelings we had long since suppressed. Kind of like kicking up mud on the bottom of a lake. Sometimes if we are not emotionally able to handle some of that repressed pain it can be blocked from entering our consciousness. We experience to a great degree only what we are able to currently handle. I think it is quite within the realm of possibility that some people step away from meditation feeling numb because a great amount of discomfort has been brought up that exists just below the surface. Until our subconscious is able to sort it out it's almost like you're on autopilot so you don't get too upset and it all comes surging up at once.