What makes someone enlightened?

Some years ago I somehow managed to stay almost the whole day without any thought, and for several months I used to be in that state of consciousness. I had the breathtaking feeling of emptiness and freedom, there were no ups and downs anymore, I was completely balanced and a profound happiness had taken me. I thought I had become a Buddha, but the thoughts started to come in and this state of consciousness faded. What makes someone enlightened? I read that if you stay 45 minutes without even the subtlest thought crossing your mind you'll be enlightened. Well, I think that is very challenging.