From the FYI column in Popular Science, August 2013, page 80:
"CAN STAYING POSITIVE EXTEND YOUR LIFE?"
I bet you've heard the studies that say a positive attitude is the difference between success and failure. Even the phrases we use, like "bouncing back" are annoyingly buoyant. So what happens if your struggles are damn hard and you don't feel like being "up" today?
Don't worry. We all have bad days. An occasional pity party day or day of rest won't set you back on your endeavor to create a new life out of the remnants of your old. Unless you stay stuck.
The article concludes with author Daniel Engber saying [italics mine], "Despite the lack of definitive data, the belief in the power of positive thinking has become so widespread that it might actually be doing harm."
Honor yourself in your struggles. If you find yourself where you can't get out of a depressed state, investigate your options with a healthcare professional.
I highly recommend pushing yourself a little past your comfort zone so that you can make incremental progress.