The Dane, who was starting his fourth game in a row, reflected the general feeling of frustration as they twice were pegged back by the visitors after David Luiz's dismissal.
"The first 30 minutes I thought we were on top," Christensen said.
"We were aggressive, we tried to control the game with a lot of energy and that worked. As soon as we got the first goal and Arsenal went down to 10 men, we had a hard time adjusting to that even though we should be able to manage, but then in the break inside [the dressing room], we said we wanted to come out with a lot of energy again and try to control it and really go for the second goal.
"We worked hard for the second goal which is why we are very disappointed that basic errors allowed them into the game.
"We worked incredibly hard to get the second goal after Arsenal had scored and we finally got it and for some reason we were not aggressive enough outside of own box at that moment [when they equalised again].
"For us it is very disappointing, we want to make this a tough place to come and play but the facts right now are we are dropping too many points at home, like today when for some reason we could not hold on to a win in the last minutes."