(Photo courtesy of Ron Finely)
Sometimes, one's falling and descent (in his Avodah) is the purpose of spiritual ascent. This is such because the whole point of falling spiritually is in order to strengthen and return, and begin anew one's vitality and his mind, because these two things are the essence of one's Avodah. The whole point is to live a new life of serving Hashem every moment.
Although it seems counter-intuitive, we sometimes have to fall before we can get up. It may be that at one moment we find ourselves to be very high, but because of that level we wont be able to climb any higher. Only when we actually fall can we invigorate and motivate ourselves to push even higher than we were before.
On the other hand, it may be that what seems to be falling is actually rising. In Likutei Moharan 25, Rabbeinu elaborates on the idea of levels having two layers. The inner layer, which radiates what one might interpret as spiritual ascent, and the outer, which could be perceived as descent (think of the outer peel and inner meat and juice of a fruit). Rabbeinu says that when someone climbs to the next level he must first encounter this outer level, which has the appearance of failure. But, that is only an appearance, and this person has actually grown, and will soon see the fruits of his struggles.