Normal magic involves carefully constructing a structure in astral space to draw the magic through. This helps prevent damage to the mage from wielding the mana, and when Drain does occur, its effects on the body are limited.
If the chips are down, any mage may choose to spend a Bennie to instead use wild magic, drawing mana directly into and through their own aura. The extra power surge allows them to cancel up to 2 points of penalty to the roll (which stacks with any other similar penalty-cancellation effect.) However, if they take Drain, then it will be a Wound rather than Fatigue.
If you roll a Critical Failure on a reckless casting, you should expect significant problems to occur…