Being moody doesn't make you an artist. But almost certainly an artist will be moody. And by artist I mean anyone who creates. Writers have writers block, painters may sit in front of a canvas for hours just staring. Closer to home, a photographer may sit and stare at their last shoot and can't see anything they want to edit.
On good days the juices are flowing, planets are in line, wine is just the right year, something. Something clicks and you wake up and can't wait to get to it. Paint flies on the canvas, words flow like water, or Photoshop is so busy your computer fan is on high. The problem is, we can't control what days will be creative. We can't put a finger on the trigger for the same reason we can't control or really predict the weather. A lot of things can stop the juices and other things give it a fist full of pulp to give you special days.
The thing that keeps me sane during the down times is knowing it happens. It's not the end, it's how it works. Of course you should worry because, as we all know, if you worry about something it never happens.
I have found that the best way to come back strong is to accept the down days and go off to do something that's mindless or at least not creative in the same way as my photography. This is often when I come up with new ideas. Write them down for a juicer day. The more I accept those days the stronger the creative days seem to be.
I also have plenty of my favorite images hanging on the wall or popping up on screens to remind me that yes...I'm a creative...maybe just not today.