The antithesis to Joy isn't Despair. They're friends, they're sisters, not opposites. Despair is what pushes us to introspect, grow, and overcome. The hard times when we resign ourselves to solitude and hopelessness, reveal our weakness and help us push past that weakness. We realize that weakness exists and must exist for there to be strength.
Take a little time. Learn about yourself. Cry and wallow in your despair. Remember, this too shall pass and you will experience joy again- more fully this time.