Don't abuse your responsibility for your bottom's safety just because the euphoria of a endorphin rush makes your bottom a little giddy. In order to stimulate the release of endorphins, the top should gradually increase the pain level until it nears the pain threshold. After reaching the threshold, lower the intensity and allow the endorphins which the pain released to work their magic, nullifying the pain. When the top once again begins to increase the pain, the endorphins which the previous cycle released allow the bottom to tolerate a higher level of pain. The now higher level of pain releases even more endorphins, and the cycle begins again.
Patience is a virtue here.
There are several difficulties you may run into. Keep them in mind, watch for them, and when they occur, alter your technique until you find that unique formula that works for you and your bottom. Sometimes subtle changes in technique can produce dramatic results. Sometimes the pain threshold will hit a plateau, refusing to rise further. If this happens, a complete break in activity for a few moments, a few minutes or longer might be in order.