Something that I have learned from my freelance work years and from just my own life is that life is made up of peaks and valleys. It does not stay stagnant. Sometimes, it can take a while to reach the next peak, but my life has had a lot of peaks that I thought would remain and didn't...and a lot of valleys that never seemed like they would end, but they did. In my freelance and other work, it has been THIS job that excelled or THAT job or THIS project or that one that would take off...and I rarely expected years before to be in that situation.
The point is that you don't know what the next peak will be, even if you are pushing towards it. Invariably, it always blooms in a way that was not expected and the surprise is a part of the good of it. So, since you don't know what the next peak will be or when it will be, why should you spend all the time leading up to it that feeling depressed... it's coming, you know it will.
So, even if you don't know the next peak, I would recommend that you look around in the valley, make buddies with the skeletons, take pictures of cactus flowers and make sandcastles in the desert. You gotta be there... so why not enjoy the journey as much as possible?