Today, I felt happy.

This is rather rare for me. Most of the time I'm either anxious, depressed, lonely or stressed. Never happy. The last time when I felt like smiling, my brain managed to think up all the lovely things that caused the anxiety and depression, making me feel that once more.

I can't stay happy. I don't know why. Something always comes up. Nothing particularly bad is happening in my life right now, other than the issues above. But I just can't stay happy. I can't not worry about stuff. It just...happens. There's no other way I can describe it. I convince myself that I'm not allowed to stay happy, that the feeling is abnormal and I should feel all depressed.

Does anyone have any ideas on how to not go back to that mindset, and actually stay happy - or at least somewhat positive and not self-loathing - for more than a few hours at a time?