Just as Personified says. Two years ago I was seriously ill, and was going in and out of coma for nearly a month. I was the same too, in that I was clinically dead for six minutes.
The thing is, I didn't know when I was in a coma or not! But I know that I had vivid dreams!
I was so near death, that when I started to recover, the Consultant told me that I could not be "brought back again" without extreme brain damage.
I now carry a DNR card.