Why may a rise in testosterone above normal cause a subsequent decrease in the hormone?

This is a question from the AQA June 15 Biology A level past paper. 

Short answer: Raised testosterone causes a physiological decrease in GnRH as well as LH and FSH via negative feedback.

Detailed answer: To answer this question one must consider the hypothalamus-pituitary-testes axis (best drawn out) and the principle of negative feedback. 

The hypothalamus releases GnRh which stimulates the pituitary to release LH and FSH. LH and FSH in turn stimulate the testes to release testosterone. Testosterone inhibits the GnRH and LH and FSH release thus high amounts of this hormone reduce GnRH as well as LH/FSH release which in turn reduces stimulation of the testes - ie less testosterone is produced.