What is the interpretation of feeling trembling and fear after asking Allah for a sign of acceptance of repentance? And is there a mistake in this request?

The enquirer's initiative to repent is commendable, and we ask Allah to accept it. The signs of accepted repentance are Allah granting the repentant person success in acts of obedience and steadfastness upon the truth. There is no harm in supplicating that Allah make a sign for the acceptance of repentance, but it is not necessary that what you feel is this sign, as it may be due to ordinary reasons such as organic illness or fear of sin. Therefore, have trust in Allah and think well of Him, seek ruqyah (Islamic exorcism), and consult specialized doctors.