Is it permissible to increase one's usual daily devotions of fasting or Qur’an recitation when one feels energetic, knowing that one will not be able to maintain this increase?

The most beloved deeds to Allah are those which their doer persists in, even if they are few. This is because the persistence in a small amount ensures the continuity of obedience, remembrance, mindfulness, intention, and sincerity. This bears fruit, yielding many times more than a large but interrupted effort. One who persists in a deed consistently engages in service, frequently returning to the door of obedience. He is rewarded for his frequent return. The purpose of commanding moderation in what one can persist in is out of fear that a person might burden himself with an act of worship he cannot endure, leading him to fail and discontinue it.