Why wouldi be having uncontrollable body jerks?

Seizures. A detailed history is needed. Uncontrollable body jerks could be seizure, if you have one side jerking and you are aware of it, this may represent simple partial seizures, if the jerking all over the body and you are fully awake, so this can not be seizure as generalized seizure causes complete brain shut down and loss of consciousness, electroencephalogram can help in diagnosis.