In order to awaken like a Jew one must go to sleep like a Jew:[1]
In order for one to wake up with the proper thoughts one must go to sleep with the proper thoughts. Thus the start of a good day which is imbued with joy and spiritual matters is dependent on the order one follows prior to sleep. Hence one should think of spiritual matters prior to going to sleep as is accustomed to do when one says Kerias Shema Sheal Hamita.
[1] Toras Shalom p. 5-6; So is the accustomed saying amongst Chassidim, brought in Arugas Bosem 1:1 in name of Rav Meir of Parmishlan; This explains why the Rama [1:1] writes that when one lays in his bed to go to sleep he should know before whom he is lying as this will affect how he will awaken the next morning.