Have read that people with chiari 1 malformations can have cerebellar fits. what is the difference betw. a cerebellar fit & a tonic clonic seizure?

No such thing: Cerebellum is a controlling part of the brain, would not likely create seizure like activities. Tonic clonic is true seizure, not just single jerking movement.

Some differences: Cerebellar fits"characterized by drop attacks with/without deterioration of consciousness, opisthotonic posturing(head and back arching backward), and varying degrees of respiratory compromise. Cerebellar fits may mimic other disorders such as cardiogenic syncope and epileptic seizures. Tonic/clonic (grand mal seizure) generalized seizure with muscle contractions and loss of consciousness.