Well then how about you fake a smile?
Although you may not be able to change your attitude, changing your behaviour by smiling can actually trick your brain into thinking that you're happy.
This will naturally cause the brain to make 'happy chemicals'. So in turn, what used to be a fake smile can change into a happy smile.
But wait, you say, you're feeling too down to fake it?
Tip: Hold a pen using your teeth horizontally, mimicking a smile; that'll do the trick.
Happy Smiling ^__^
Miss Eliza WonDerland <3