I have those day as well, I can't stop stressing about money, my to-do list, and sometimes I just don't have the desire to do anything. I have come to accept these days as a normal part of life and learned that if I embrace them rather then try to act like everything is OK they it gives me time to regroup.
Embrace those bad days. Start by taking inventory of your blessings, and the good things around you. Then let the day just happen. The day will pass before you know it and soon you will feel like yourself again.
You can't know happiness if you don't know sadness, and those bad day show you your strengths and weakness and what you need to move forward.
Once you realize that those bad days come and go and they are a normal part of life, you can take the steps needed for it to pass quickly, leaving you ready to take on the world!
Do you embrace your bad days?