Daniel Wu revealed that his wife Lisa S. was pregnant while he was busy filming That Demon Within.
His busy schedule with the film meant that he could not be by her side. As a result, he was guilt-ridden throughout.
It did not help that his character was dark and depressed as well.
The combination of factors caused him to lose lots of weight -- up to 18 kg according to some sources.
He said, "At the time I have a lot of pressure. I could not talk with anyone else. A lot of strange ideas surfaced as well. Thus as soon as the shoot was done we went to South Africa for a vacation to leave the character."