My pastor spoke about this topic several Sundays ago and he said the same thing that
Jasher is basically saying..... That if you are concerned about having done it, then you haven't. Blaspheming the Holy Spirit occurs when a person knows, and then chooses to do it. The way that it eternally separates you from God is because when you turn your back and blaspheme the Hold Spirit, then you separate yourself from him. My pastor talked about how the Holy Spirit whispers to us in that still small voice, and we listen and hear it. But when you Blaspheme, you are continuously shoving away the voice until you can no longer hear it. So, you become eternally lost because you can no longer hear the voice, and you continue down a path of destruction.
My Pastor gave a funny story about when he was a kid and they would "play church." He said he always wanted to be this lady who was in his church because she would get up in the middle of service every Sunday and start making a ruckus because she was overcome by the Holy Spirit. So, when they would play, he would always be that lady. As he got older, one Sunday he heard a sermon on Blaspheming the Holy Spirit and he was suddenly scared. He was afraid that by mocking this lady all those years of his youth that he had now committed the unpardonable sin. That was when he learned the truth. That it is not those who do so out of ignorance or innocence. It is those who know the spirit and then choose to do so. Blasphemy is about making a choice. It is that choice that makes the sin unpardonable, because that choice makes you completely numb and deaf to the Lord.
I hope I explained it all right.

If not, then I hope that God will help you understand what I am trying to explain in my poor attempts at explaining.