What is the cause of the intense dread and insomnia that leads to difficulty sleeping, and fear of it, bearing in mind that the questioner previously felt someone choking her during sleep, and that stopped after she recited the Quran?

Every affliction that befalls a Muslim is a means by which Allah expiates his sins. The first step towards healing is sincere repentance and seeking forgiveness, followed by steadfastness in obeying Allah and fearing Him. For whoever fears Allah, He will make for him a way out and provide for him from where he does not expect. A Muslim must sincerely turn to Allah and rely on Him, and be persistent in supplication, reading the Qur’an—especially Surat Al-Baqarah—and increasing in acts of obedience such as charity, remembrance of Allah (dhikr), prayer, and ruqyah shar'iyah (Islamic incantations).