This happened one day during recording when Kris’s and Minseok’s body conditions were not so good. Minseok seemed to have been having a painful ache in his chest. When the recording was over, Luhan walked up to him and playfully hit Minseok’s chest, but Minseok fell down from his (standing) position and cried out badly (maybe because it was too hard to bear the pain).
Luhan felt so sorry he hugged Minseok (who was still on the floor) while apologizing repeatedly and he soothed him after that.
After the accident Luhan took care of Xiumin very carefully and kept Minseok by his side.