It is the activation of you life force your qi your prana. This energy flows through your body and breaks through physical and emotional blockages. The opening up can be experienced in shaking or spontaneous movements of the body or the expression of emotions like crying, shouting, laughing. The energy itself can be felt as a vibration, hot flushes or a cold rush moving through the body.
After the session you might feel different. Maybe some physical pain is gone, maybe some things that used to trigger you in your life are not affecting you anymore. And much more. Every session is different and everyone will experience it differently.