^ This overamping thing is a serious misconception. Your brain wont just "shut off" to protect itself from a dose of amphetamines. If this were the case then it would work for cocaine, MDMA, MDPV, and every other stimulant out there. If you take too much amphetamine you will overdose.
The loss of consciousness (LOC, syncope) is due to increased oxygen demand caused by the increased cardiac output. This can cause the heart to have an arrhythmia eventually leading to ventricular tachycardia (VT), which results in the heart shutting down and syncope by association. All of this is caused by the body releasing massive doses of serotonin and even more importantly norepinephrine.
This is a serious situation that should be brought to the attention of the Emergency Services immediately. If you feel like you like you are going to lose consciousness after taking amphetamines, call 911. It can very well result in a stroke, brain hemorrhage, or cardiac arrest of not treated immediately. There is no "overamping".