This is my Hmmm. Something about that sentence isn't quite right face.
Things can escalate quickly, when you're stuck in a silent room with a disastrous manuscript and no idea what to do about it. In the early days I'd go quite crazy when things weren't coming together (and as a general rule, it takes about a year for things to come together. So that's a lot of crazy.)
Writing is my job; I have deadlines and contractual obligations. Crazy puts all of those under threat. It also diminishes the quality of my work and makes me think I dislike writing. (I don't dislike writing.) Staying positive and calm, therefore, have become as important to me as owning a computer or eating my lunch.
I think there's a lot of guff out there about positive thinking. It's not about smiling joyfully through a bereavement, or congratulating the person who just mugged you. Nor is it about squashing down valid feelings, or pretending things are fine when they are not. Positive thinking is simply about getting into the best possible mental state for the situation you're in. The most helpful state. The most appropriate state. And as a general rule, tearful hysteria isn't a helpful or appropriate response to a plot problem - I've tried it enough times to be certain. Grim determination might be the best you can manage, on a day like that, but it's a lot more helpful than the alternative.
I won't go into the tools I use to stave off the crazies. They're just what works for me, and everyone's got some way of lifting their mood: meditation, affirmations, music, doughnuts, yoga, phone calls to good friends, NLP, visualisation - if it works for you, it's the right one. The important thing is to do it!