The poet and grammarian Bhartrihari in about the 7th century A.D, pays tribute to Patanjali and the efficacy of Yoga through this line of a shloka (verse):
Yogena cittasya padena vacam
Translation : Through Yoga, serenity of mindWhen people start practicing Yoga , they have different expectations with it. Although, Yoga is a holistic science affecting Mind and Body, positively; but still one sure consequence of Yoga is Peace of Mind. And this consequence doesn't take much time to manifest itself. Within the first week of of your Yoga practice, you will feel serenity of Mind. A peace of mind which helps you see yourself and the World in a different Light.