To explain further, we need to use some more technical terms to leave no doubt. Come on: during exercise, there is an adaptation of the cardiovascular system to promote increased blood flow primarily to the muscles. The heart increases the so-called cardiac output which is the volume of blood pumped circulation per minute.
The blood vessels supplying the muscles, undergo dilation to permit a greater amount of blood to carry oxygen and nutrients higher energy production. This situation of increased blood flow and vasodilation of the vascular bed persists during the activity and will only be changed when the exercise ends. When finished the activity, the faster change that will occur is the reduction in heart rate and consequently a very rapid decrease in cardiac output with reduced blood flow. At this time the blood vessels, especially the muscles of the lower limbs are still dilated because the vasodilatory effect of exercise still persists for some time after the end of the activity. If there's already an abrupt halt, the blood slowly returns of the lower limbs, especially because it ceases to exist the "pumping" of the muscles contracting.
This is the main cause of the sudden drop in pressure which can cause dizziness and even fainting. A clearer way, we are with our hearts full steam circulation of blood throughout the body whenever we demand more of our "machine". So when we stop suddenly, the heart also gives a stop and tries to slow along with you, reducing the demand for blood in the blood vessels and causing this discomfort and possible fainting.
So guys, no "get coming" and stop once we take that well levinho trot at the end of training and tests, just to make sure nothing goes wrong with our body. If you are a hard training, make the final minutes one slowdown and go gradually stopping, if a test, try to take advantage of that straight after the porch of arrival to a light trot to pick up your water and finisher medal.