This process regularises your body functions, reduces tension, improves blood circulation, improves oxygenation of the body and promotes your healing and recovery.
Gradually you feel your mind becoming still. You become more aware of the sounds smells and movements around you.
Gradually this too fades away and you enter another state of consciousness. The experiences here do not co-relate with what we already know.
Do not be afraid. Just observe, without seeking to categorise judge or classify what you see through your mind.
As you continue with the yoga, the experiences change, and change again.