A long time ago, I realized that attitude is half the battle in most anything you do or encounter in life. Internally and externally. Let me give you some life examples.
Externally: Project the attitude that I belong here and I know what I am doing.
I could walk the halls at school, go wherever I wanted and never be questioned by teachers and staff I passed because I wasn't giving off the scared rabbit vibe or the sulking bad girl vibe.
Externally: Project confidence and defiance when needed.
I worked with a young woman 25 years ago that came running into the office out of the warehouse in tears because a warehouse worker said “I'd love to get me some of that .” ,when she walked by. She was shaken. I couldn't grasp where she was coming from. Usually no one ever said anything like that to me or within my earshot. But on the rare occasions when they did, I either met their gaze with a face of stone or I casually called over my shoulder, “in your dreams!” Depending where it happened, who they were, who else might be around and such. I never had the thought for even a minute that I should crumple and cry or shriek like a rabbit and run.
Internally: Tell yourself you are tired, lazy, sick, etc.
You'll get nothing accomplished and later or tomorrow feel even worse because things have stacked up and you feel overwhelmed and still tired, sick, lazy, etc.
Tell yourself I've got to get my butt moving, I want this done, it's a beautiful day for this, etc.
You'll be surprised how much you actually do get done before you quit for the day. The next day, there's a little less to do and you actually do feel better because of it.
These may not be the best examples of what I am talking about, but I think you get the idea. If you haven't tried it before, please give it ago! If you have, tell me how it went for you.