The end of a workout is an essential aspect of all cardio workouts. Whether it is a step class, indoor cycling or running, all cardiovascular exercises require an active recovery period.
The cool down phase is assumed to contribute to less muscle cramping and stiffness. It also prevents hypotension ( low blood pressure, resulting in dizziness (due to the lack of blood flow back to the heart and brain because blood is being directed to the legs), which may occur when suddenly stopping exercise.
Inadequate blood return though out the body causes blood to pool to the lower extremities; this can cause insufficient blood flow to the brain which may result in dizziness and faintness.
It is for the above reasons that it is recommended that a 5-10 minute cool-down be performed for all cardio type workouts.