How can psychological security be achieved and extreme fear of death and its agonies be overcome, with reference, please, to how to win God's promises in His saying: "The angels will descend upon them, [saying], 'Do not fear and do not grieve but receive good tidings of Paradise, which you were promised'"?

Fear of death is praiseworthy as long as it does not reach the point of despair and despondency. However, fear of loneliness is not praiseworthy because the believer finds comfort in Allah during his solitude. Not laughing out of fear of death occurred to many of the Salaf. If this fear leads to a pathological fear that reflects attachment to this world and turning away from the Hereafter, or causes psychological distress and isolation, then it requires behavioral psychological treatment and consultation with a doctor.