Maybe this is a wrong context to ask this question. Can someone tell me what exactly is a mystical experience and how it differs from normal human experience. When does one consider himself enlightened?
A mystical experience happens through unity, an everyday human experience through duality.
Duality is when you unconsciously make a distinction between you and your thoughts and perceptions. "I think therefore I am" is the subject observing his thoughts, this is duality.
When you silence your mind, you just are and then there is no opportunity for you to define yourself, to make distinction between what you are and what you're not. "I am all that is" is the subject realizing there is no separation between him and his perceptions, this is unity.
Yoga is one systematic way of cultivating this silence that is required to access those mystical states of mind.
As for enlightenment, I could not say because I'm not ;).
That's a legitimate question! Part of the whole problem in this field of study is that there's no widespread agreement on even such basic things; everyone has their own idea and no sound research has been carried out to establish what it is we are even talking about.
I could talk at length on the subject but I couldn't do it any better than Gopi already has; you should check out "The Real Nature of Mystical Experience"
