My beloved Shri Anandi Ma
This leads to an interesting quandary.... If kriyas start on their own and are caused by energy, how come you can stop them with your mind? The answer, as I have understood it, is simple: Ask and you shall receive. That's why. As disciples of an enlightened being, we are instructed to pray to Anandi Ma for help to stop these. This works.
Kriyas can be disturbing though. When your body is flinching, shaking, or trembling we automatically think of the central nervous system. This is correct even when analyzing this completely weird part of spirituality because the sushumna lies near the spinal column and the ida and pingala wrap around the sushumna. The Kundalini's shakti winds it's way up towards the crown and sometimes Her shakti is so powerful that is is released through other parts of the body. This is nothing to be scared of or disturbed by.
(I bet if you are not a yogi, you are surprised to recognize this symbol! Yes, this is the sushumna, ida and pingala. Amazing, huh?)
One case of kriyas that I always think of is Swami Kripalu. His sadhana (personal, spiritual practice) created so much prana that it was violent at times. He practiced behind locked doors, only allowing a select few to bear witness. He often came out battered and bruised. This neither scared nor phased him. It only brought him closer to enlightenment. Also consider American religions; Shakers and Quakers. Kriyas are how they got their names. The often shook during prayer.
So you may someday find yourself quaking during class, meditation or prayer. Have no fear. Feel free to shake what the good Lord gave ya'!