"I did wish today that I would see this," Klopp told reporters. "It was our worst half in the Champions League in the first half, we showed nerves and it was not good at all.
"In the second half we tried better but they were very clever. Over the two games we are deserved winners. I cannot describe what I was feeling inside, I think I need to see a doctor. If we play with the passion of tonight we are difficult to play against.
"We are in the semi-final, it's one of the best nights ever. Me and my assistant were talking and saying to each other 'who would have thought a couple of years ago we would have been in the semi-finals of a Champions League'?"
The first leg between the two sides in Spain last week ended in a goalless draw.