The hosts were living off scraps and rarely able to get out of their half but they were presented with a glorious chance to reduce the deficit five minutes before half-time.
"Any goal from any our players would have been great especially after we created so many chances in the second half".
"Myself, Lars (Lagerback, Norway coach) and the medical team discussed it and agreed that I should go home to get fit again a quickly as possible", the 25-year-old added.
O'Neill's side head to Norway for their final Group C tie on Sunday evening with six players - captain Steven Davis, Stuart Dallas, Oliver Norwood, Josh Magennis, Jonny Evans and his brother Corry - on a yellow card.
They face Norway on Sunday but the more important fixtures will be the two-legged playoff against an opponent as-yet undecided in November.
The hosts conceded twice inside 21 minutes and were fortunate to only be 2-0 down at half-time, goalkeeper Michael McGovern and the woodwork both denying Germany. "3-0 would have been harsh, we deserved the goal in the end, but it was very hard".
"In September 2016 we looked at our group and told ourselves we wanted to dominate that group, make no compromises and possibly not drop any points either, which we've managed to do with a neat goal average to boot". We clawed our way back in and what we gave in the second half was fantastic. We have to make sure.
The presence of Kimmich effectively as a right-sided forward was nothing new to Northern Ireland - they witnessed it at Euro 2016 - but Chris Brunt at left-back simply could not cope.
Northern Ireland should have made it 2-1 with 15 minutes remaining after the industrious Magennis got the better of Mats Hummels and set up Washington whose rising effort struck the crossbar. Equally, it would be nice to go through this campaign and say Germany are the only team that has been able to beat us'. The quality they have and the positioning they take up and how they play is absolutely ridiculous. I thought the players were excellent against Germany and the referee was very good.
Sebastian Rudy, whose brilliant second-minute strike from distance set the Germans on their way on Thursday, has warned the other countries hoping to lift the World Cup in Russian Federation that the current holders do not want to hand it over.
"Perhaps we could have done better, but the quality of the strike was phenomenal".