Is it wrong to excessively think about the death of one's parents, when such thoughts cause distress and fear?

Every soul that has been breathed will die. Therefore, one must submit to Allah's decree and be patient upon the death of one's parents. If they were righteous, supplicate to Allah to unite you with them in Paradise, and adhere to piety so that you may join them. If they were not righteous, advise them without failing in your dutifulness to them. In all cases, offer sincere supplications for them during their lives and after their deaths, and treat them with kindness.