What is the interpretation of trembling, feeling heavy and in pain, and one's head lifting off the pillow, after reciting "I seek refuge in Allah from every devil, and every poisonous creature, and every evil eye" and before sleeping? And what is the relation of that to shortcomings in worship?

The nature of what happened to you cannot be definitively determined; it could be a temporary illness or something else. It is advisable to maintain obedience to Allah and avoid disobeying Him, not to miss prayers, and to beware of letting your gaze fall upon what is unlawful, in compliance with the Almighty's saying: "Tell the believing men to reduce [some] of their gaze and guard their private parts. That is purer for them. Indeed, Allah is Acquainted with what they do." One must also perform Ruqyah (exorcism) upon oneself using the authentic incantations and invocations transmitted from the Prophet (peace be upon him).