What is the cause of recurrent nightmares and the sudden sensation of an electric shock, despite maintaining prayer and remembrance (dhikr), and is ruqyah (Islamic exorcism/healing) sufficient to overcome this?

No definitive conclusions can be drawn from these disturbing dreams. Satan may toy with a person to harm them and cause them distress, and such dreams are a type of vision. They could also be an indication of the evil eye, jinn possession (mass), or sorcery, especially if they recur. In such a case, spiritual protection (tahseen) and ruqyah (Islamic exorcism) are among the best remedies. It is preferable for the person to perform ruqyah on themselves, or to seek a righteous and upright raqi (exorcist) while adhering to Islamic guidelines. One should also frequently make supplication (du'a) and implore Allah the Almighty.