It all depends upon the individual person. There are people who fear becoming old because they fear losing their looks, youthfulness, mobility, independence, & cognizance. They view becoming old as becoming more dependent upon others. There are others who fear death as death is the great mystery. A subcategory of this is that there are people who fear death because they don't want to go to hell as they contend that they were quite imperfect.
There are people who fear losing their jobs hence socioeconomic status thus slipping into poverty, even homelessness. They see poverty & homelessness as the end. They will do anything to hold on to their jobs & their respective socioeconomic status. The wealthy fear becoming middle class & the middle class fear becoming poor, even impoverished.
There are women, especially beautiful women, who fear losing their beauty. Those who are affluent will resort to plastic surgery to retain their looks as their looks are instrumental in retaining their high-powered careers, lovers, & husbands. Those who are poor will see their looks fading as they don't have the funds to retain their looks. There are women who fear losing their husbands as their husbands are the psychological & oftentimes socioeconomic bulwarks of their families. They feel that if their husbands leave them, their world as they know it, will be finished.
There are religious people who worry about going to heaven if they die. A few among them even fear that they will go to hell because they have been indoctrinated that they were sinners w/little or no hope of redemption. As a result of such fears, they live their lives in fearful, purgatorial, & even infernal apprehension.