It can be all too easy to feel as though our emotions and bodies are working against us, creating anxiety, sense of unease/foreboding and worry when we are trying to get on with our day and "feel positive and happy!" It is important to remember that humans are built for survival, not happiness, and that your body is simply trying to do its best to help you survive, no matter how uncomfortable or inconvenient these experiences might be.
A recent tweet by Dennis Tirch succinctly nails this important point. See further work by Bruce Perry (eg YouTube video below) for more information.