At some point in each of our lives we have experienced physical tiredness. These are times when we are simply tired from too many activities or difficulties in our lives.
When you experience spiritual fatigue, it is because of a wrong view of your faith. You will find yourself keeping a mental checklist of dos and don'ts, working hard to please God with religious activities. That is not freedom. The Christian life is not some mystical formula where you alter your behavior to receive the Lord's approval. The last time I searched the scriptures it indicated that God reached down and reconciled each of us to Himself the moment we partitioned Him into our hearts, so you already have His approval.
Genuine spiritual maturity involves a growing awareness that nothing you can do, no change in behavior or attempt to live a certain way, will make you acceptable. Instead, you surrender your inability and weakness, and live by faith. At that time God's omnipotence will carry you through life.