As the muscles begin to relax and the pressure is released from previously numbed nerves feeling begins to be restored and is felt as pain. This is a positive sign indicating that communication between the brain and body is being restored.
You may also feel very tired at first as the body uses its energy reserves to restore and regenerate itself. You are advised to try and get a bit more rest and stay hydrated as the body undergoes the process of releasing the built-in stress.