Were Medieval Flagellants (certain people on pilgrimages) committing a sin?

All things are possible within the bounds of human nature and to answer for everyone who practised self mortification would be impossible,but in defence of self mortification Jesus said this``If your right eye causes you to sin, gouge it out and throw it away. It is better for you to lose one part of your body than for your whole body to be thrown into hell.(Matthew 5:29)