Does dystonia get worse over time?

Depends. Dystonia is a neurologic syndrome characterized by sustained involuntary muscular activity producing sustained, abnormal and repetitive muscle contractions causing twisting movements, abnormal posture and functional disability. There are many different types and causes with different prognoses. Some remit, some stay the same and others get worse.
Rarely. Most dystonia is focal, aggravated by overuse and not by age. Some neurological diseases have dystonia which gets more difficult to treat because of contractures over time. Botulinum toxin injections are useful for months of relief without medications in some cases.