The result of doing a spell for which one does not have enough "onboard" energy to adequately meet the spell's energy requirements. Normally backlash in humans takes the form of generalized fatigue, often associated with a cluster of symptoms like headache, body aches similar to those caused by muscle strain, and shortness of breath.

The physical symptoms are due to the fact that the simplest way in which a wizard is "charged" the price of a spell is normally a deduction of their available physical energy. The wizard's mind and body then react as if the wizard had actually undergone the kind of physical stress necessary to cause such an energy loss. For this reason, many wizards past the first flush of their power (i.e. out of adolescence) get in the habit of regular and sometimes strenuous physical exercise, as working out leaves the frequent practitioner with a body better able to recover quickly from the stress of wizardry, and a mind better prepared to quickly shake off the backlash. Many of the most accomplished wizards have unusually active sports lives, or spend a lot of time in the gym.

However, even such preparation is not sufficient to cope with the backlash from some spells, particularly psychotropic spells which have a direct effect on the mind of another being or beings. The aftereffects from these spells are routinely the most severe. (SYWTBAW et seq.) See also: Games wizards play: Mind-body interface: Wizardry, prices of.