釋禪波羅蜜次第法門 3.24

3.24

令繫心頂上者，為心沈惛多睡故，在上安心；若久久，即令人浮風，乍如風病，或似得通欲飛，有此等過，不可恒用。

Having one fix the mind on the crown of the head is because when the mind is sunken, drowsy, and prone to sleep, one pacifies the mind above; if done for a long time, it causes one to have floating wind, suddenly resembling wind disease, or appearing as if one has attained supernormal power and wants to fly; because of these faults, it cannot be used constantly.