Very simple. Just say fuck it. Say it out loud. Stop thinking like that. The world is as nice as you make it, and you're only making it worse thinking like that. Smile. Smoke. Enjoy being alive, and find out what is causing the anxiety in you. Depression is a medically proven chemical imbalance in the Limbic System of the brain and you should see a doctor if you feel like that all the time. Try my method, if that doesn't work, see a doctor. Sometimes pot only exacerbates existant medical conditions.