Are there death throes and terror from it and from the resurrection that even a believer experiences, so where is the mercy in that?

The throes of death and the hardships of the Day of Judgment for the believer are good, either for increasing reward or expiating sins. The believer is given glad tidings of Paradise and rejoices at meeting his Lord. As for the disbeliever, the hardships of death and the Day of Judgment come to him as torment, and he dislikes meeting his Lord. The believer is safe from the terror of the Day of Judgment, and the hardships of that day are among the expiations for sins. And Allah is Wise, Just, and Merciful; His actions are based on profound wisdom, and He is not questioned about what He does. It is incumbent upon the Muslim to submit to the commands of Allah and not question the details of the wisdom therein, for Allah has decreed mercy upon Himself, and His mercy is vast, having overcome His wrath.