The Da Vinci Code's bloody depictions of mortification are grotesque exaggerations that have nothing to do with reality. Obviously the movie makers were looking for shock value, and the real use of the cilice and discipline would have been too tame. In reality, they cause a fairly low level of discomfort comparable to fasting. There is no blood, no injury, nothing to harm a person's health, nothing traumatic. If it caused any harm, the Church would not allow it.
See this video with Fr. John Wauck on this