I have no scientific research to back this up, but I suppose you can tell when dopamine is released. It is when your mind likes something so much that it totally focuses on it and you forget about everything else happening around you. This happens when you PMO or when you watch a good movie or when you take a walk in nature or follow a hobby. It can be a positive or a negative thing. It is up to you to judge based on the situation. May be it is generally bad when you know that what you do is making you less sensitive to the real world. Dopamine release is good and natural, the bad thing is overstimulation and addiction. EDIT: This post is a little speculative.
