I often find that the quality of my meditation goes up and down. I always hope that I will not fall down again, but it happens constantly.
In the beginning everybody experiences ups and downs in the spiritual life. When a child is learning to walk, in the beginning he stumbles and falls again and again. But after a while he learns to walk properly, and finally to run. Eventually he can run as fast as his capacity will allow. But a small child cannot expect to run as fast as his father does, because his father has much more capacity.
You experience ups and downs in your meditation. When you are up, you have to feel that you are getting a glimpse of your eventual capacity. When you are down, you should simply feel that this is only a temporary incapacity. Just because you see that those who are more advanced than you in the spiritual life are running, you must not be discouraged. Once upon a time they also stumbled.
Right now the sky may be full of clouds, but a day will come when the sun will shine again with its full effulgence. When you experience low moments of fear, of doubt, of lack of aspiration, you should feel that these won't last forever. Like a child who has fallen, you must try to stand up again. Someday you will be able to walk, then run, and finally run the fastest without falling.