Ibn Qayyim (r) said: "When the slave wakes up as the night encloses upon him and his only concern is Allah and how to please and obey Him, then Allah takes upon Him to fulfill all of his needs and remove from him all that causes him anxiety. Allah also makes his heart free to love Him only, his tongue free to remember Him only and his body free to serve Him only.
However, when a slave of Allah wakes up when the night encloses upon him and his main concern is the world, Allah will make him bear the burdens of it's anxiety, grief and hardships. Allah will entrust him to his own self and He will make his heart busy, stealing from it His love since it will be preoccupied with love for creation. Allah will keep his tongue from His remembrance because it will be engaged with His creation; his body will be kept from obedience since it will be enslaved by its desires and services. And he will toil like a beast of burden toils in the service of another. And all who turn away from the worship, obedience and love of Allah, will be put into trial with the worship, service and love for creation."
Allah (the Exalted) says:
"And whosoever turns away (blinds himself) fromt he remembrance of the Most Gracious (Allah) (i.e. this Qur'an and worship of Allah), we appoint for him Shaitan to be a Qarin (an intimate companion) to him. (Qur'an 43:36)
Ibn Qayyim continues to say: "Seek out your heart in three situations:
-When you are listening to the Qur'an
-When you are part of a gathering of remembrance
-When you are alone and away from the world and it's distractions.
If you cannot find your heart in these three situations, then ask Allah to bestow upon you a heart, for indeed you are bereft of one."