Is it possible for Allah to inspire one of His servants in such a way that he is among the disbelievers whose limbs will testify against them on the Day of Resurrection?

We do not have what definitively proves the reason for what you claim is happening to you. You must dispel the delusions of falling into disbelief andDistance yourself from the whispers of Satan. Indulging in obsessive whispers increases hardship, so you must seek refuge with Allah from Satan and his whispers, as the Prophet, peace and blessings be upon him, advised: "O Allah, Creator of the heavens and the earth, Knower of the unseen and the seen, Lord and Master of everything, I bear witness that there is no god but You. I seek refuge in You from the evil of my soul and from the evil of Satan and his polytheism."