This question is particularly directed to those of you who are wiser and more experienced in meditation than I. Recently I have made some (what I believe to be) improvement in my meditation practice, particularly in my concentration ability. What has been happening lately is that, after my concentration focuses and deepens (and my attention ceases to "stick" to the past or future, at least to a degree far less than usual), I will begin to feel a great warmth, tingling, or buzzing feeling in my body (usually beginning somewhere in my chest or torso). While maintaining concentration, I am able to control this feeling, intensifying it, spreading it around, or stopping it completely. If I choose to intensify it and spread it throughout my entire body, it can produce some very pleasurable feelings. Sometimes the pleasure/feeling can be very mild and subtle, or very intense and coarse, but I notice that I can control this to some degree. If I lose concentration, it will end immediately. After it ends and I come out of meditation, I notice that the effects -- a calm, clear, and focused mind, a lack of many negative feelings, and ease of concentration -- will last for a while, perhaps for a few hours.
Since it is difficult to describe a lot of these experiences to a great degree of accuracy, it may be difficult to convey exactly what is happening here. I hope that I have not placed too much attention on mere distractions, and too little attention on what is important. I ask, should I continue to develop this high level of concentration and dwell in the pleasurable feelings, refining them? The feelings seem to serve as a 'shield' to things like pain, ill-will, and drowsiness, so it can be useful. I feel as though the deepness of concentration, the coarseness and intensity of the feelings of pleasure, and the length/duration at which they last could all be improved to a considerable degree. How do I know if these feelings are simply distractions?