Fortunately, Kingsley, the Minister of Magic, knew about flashbacks and what they could do to someone. And let's not forget, it was the ministry's fault in the first place. They said Draco had to be healed in 10 sessions, no matter what. But there was no way in hell, someone could manage that feat. Anyone else? No problem, but Draco Malfoy? It's common sense he would need at least three rounds of block therapy. 