What is the ruling on intense fear of kufr (disbelief) or fitna (tribulation) at the time of death, and can one be saved from that, and does the dying person possess sufficient consciousness to understand what they say and believe?

Fear of a bad ending is a good thing, but it should be a healthy, productive fear that drives a person to strive for sincerity to God, purify their inner self, and improve their deeds. For God is just and does not abandon those who turn to Him. The greatest means to avoid the trial of death are to attach one's heart to God, to have a good opinion of Him, to ask Him for a good ending, to seek refuge in Him, glorified be He, for steadfastness upon the truth, and to frequently remember God; for a servant dies upon what they lived upon.