Is the remembrance (dhikr) recited before sleep, "O Allah, I have submitted my face to You... and Your Prophet whom You have sent," contradictory to the remembrance of Allah thereafter, such as seeking forgiveness (istighfar) or praising Him (hamd), for someone suffering from insomnia, and should the remembrance be silent or aloud?

There is no objection to making seeking forgiveness (Istighfar) and praising Allah (Alhamdulillah) the last words one utters before sleeping, after the aforementioned supplication, as this has been narrated in some Hadith reports. The report from Al-Kushmayhani indicates that there is no impediment to reciting other legitimate remembrances (adhkar) before sleep after these supplications. And praising Allah and seeking forgiveness are among the remembrances for sleep.