Take a deep breath. You don't have to crank it out today. You have to be open to let it come. If you want to take your writing seriously, take a few minutes.
Everyone needs a break from time to time. The mentality "always on" sounds cinematic, but it's dangerous!
You still have time. You’re not too old, you haven’t spent your final chance. I personally don't think you have to be sad to write a sad song though. It is true that in the hardest times of our lives we come up with some of the best stuff to write.