Perhaps you have felt that emotion when a parent or your spouse moved away after a divorce, when you broke up with a boy- or girlfriend, or when you moved away from your old neighborhood. There's a feeling of separation and loss. Only a person who never loves never grieves. When you love someone, you feel a oneness and fulfillment with that person. The relationship is over and that strong emotion of love mutates like some hideous sci-fi monster into equally strong grief.
Love expresses emotional oneness, grief expresses emotional separation.
It's natural to feel up one day and down the next. The strong feelings of grief may seem frightening when we first feel the full force of this powerful emotion. Each person, however, responds differently to a single death. In the case of a famous person, the grief may be very short-lived since you didn't know them personally. Here are some general patterns in how most people experience grief.