No, you dont have to be in a bad mood to compose some dark music, even when you're happy you can compose dark themed songs, well I can! :) I love this! I love dark music, because it has something cools in it. The first 2 melodies of the strings do remember me of the james bond music theme or something. It sounds similar to it. lol.
Also, same to me; whenever I want to compose a genre, it does sometime turn out to an other genre/theme.
And ofcourse you may be proud on this one! Good work dutty! Love it!