Lennon's men took a 2-0 lead into the second leg of their play-off against the Swedish side and
Two minutes from time
Asked how he would describe the result with regards his managerial career, the Hoops boss said: "It is the best. I have been to hell and back in the last seven weeks trying to get this right.
"There is a fear factor and I lived with that. I am thinking of the ramifications if we don't go through, what it would mean for me personally, how I would get through it and how I would get over it.
"That was part of the build-up. Everyone had us in the Champions League but in the back of your mind there is always that worry, that fear.
"We have overcome that and dealt with the two qualifiers very well
"It is a great night for me personally and a great night for the players. It is not often I pat myself on the back but I am going to tonight.
"It is one of the hardest challenges I have ever had in my life and the pressure going into this game was huge. I have never experienced that in my playing days and I am so happy
"It is a minor miracle we qualified. The squad is so thin but we have a good core of players and I am very proud of them."
Celtic will be in pot four for the draw and Lennon will not mind being put in the same group as either Manchester United, Manchester City, Chelsea or Arsenal.
"That would be great," he said. "That gets the juices flowing, you know, the Battle of
"I have some great recollections of
Smiling, Lennon added: "If we can avoid Barcelona and Real Madrid, we might have half a chance. But it doesn't matter.
"I have no idea how we will do but for the players to play at the big table again is great.
"It will be very exciting tomorrow, we will all be glued to the television.
"The expectation going into this game tonight was huge, it won't be so big going into the group stages.
"So from that point of view the pressure is off."
Lennon expects to bolster his squad in the next few days.
The former Celtic skipper said: "We will have a couple lined up and hopefully we can get the medicals done.
"I don't know how many, my mind has been occupied for today's games but I will chat about it tomorrow.
"There could be bundles coming in all wanting to jump on the bandwagon but first and foremost my priority is to these players."
Helsingborg coach Age Hareide had a moan about Hooper's goal but admitted the better side had advanced into the group stages.
He said: "Celtic won and deserved to go through but we were struggling with the set-pieces.
"I think over the two games, we were too small. Celtic players had an advantage, scoring three goals from set-pieces.
"The first goal tonight was at least one yard offside and even the Scottish press have to see that.
"We almost had the same possession at Celtic Park which we should be proud of but we weren't sharp enough."
As for Celtic's chances in the group stages, the former Norway boss said: "The best teams in Europe are better than Celtic but Celtic will get better.
"They have some match winners and are always strong at home so it depends what group they go into.
"And with this fantastic crowd behind them they could pick up points, absolutely."
UEFA Champions League
Borussia Dortmund has confirmed Mario Gotze will miss the Champions League final against Bayern Munich at Wembley on Sunday (AEST).