On the Ten Days of Repentance

Why repent out of worry and trembling of the day of death? It is better to repent joyfully, anticipating the coming redemption!

The first ten days of the year, beginning with Rosh Hashanah and ending with Yom Kippur, are called "the Ten Days of Repentance." But the commentaries liken the seven days between Rosh Hashanah and Yom Kippur to Chol Hamoed - as if they were intermediate days of a joyous Festival. How can these days of awe be joyful days at the same time?