What happens if I miss a dose of follistim/antagon?

Missed dose. You must let your doctor know asap. Antagon is a gnrh-antagonist to prevent premature ovulation, and timing is critical; follistim is a gonadotropin for ovarian stimulation and missed doses may be less critical than with antagon, but can still have huge impact on a stimulated cycle.
Tell your doctor. Tell your doctor immediately when you discover that you missed a dose. The outcome will depend on how many hours the dose id delayed.