In order to avoid a roller-coaster Christian life we need to have some real things to hang onto in our times of emotional instability - things such as God's promises ("Surely I will be with you always, to the very end of the age" - Matthew 28:20) and his warnings ("No one who puts his hand to the plow and looks back is fit for service in the kingdom of God" - Luke 9:62). It is also important to have a philosophy that keeps us from ups and downs. I call my philosophy reality thinking. I know some days are going to be cloudy and some days are going to be sunny, so I won't be depressed when things aren't as good as they were yesterday. We need to realize that just as there are hills and valleys in the geography of the land, there are good days and days that aren't so good in our lives. If you're experiencing depression, ask yourself if you're holding onto some expectation that isn't being fulfulled. If so, go back and check whether or not your expectation is realistic. Mild depressions are normal. They're part of the ebb and flow of life. Sometimes we feel depressed simply because we're tired and we need to rest. One thing I tell myself when I'm feeling a little down is that I've never seen a roller coaster that only went down and never came up again.
Avoid a Roller-Coaster Faith by Robert Schuller