What is the way to get rid of the whispers of insulting God, threatening Him, feeling a desire to do so, and the resulting self-hatred and deterioration of one's psychological and physical state?

What you are suffering from is a deception and whisper from Satan. The cure for it is to turn away from them and not pay attention to them. Whenever Satan casts these whispers into your heart and makes you imagine that you are cursing Allah the Almighty, turn away from his whispers and ignore what he casts into your heart. Seek refuge in Allah from his evil, and try to think of something else. Know that these whispers do not harm you and do not affect the soundness of your faith. We advise you to go to a trusted psychiatrist, in obedience to the Prophet's (peace and blessings be upon him) recommendation to seek medical treatment.