This trial aims to test if occipital nerve stimulation (ONS) can effectively reduce pain in patients with chronic trigeminal autonomic cephalalgias (TACs), especially cluster headaches. The treatment works by sending electrical impulses to the nerves at the back of the head to block pain signals. The study will compare different treatment periods to see if patients feel better with the actual treatment. Occipital nerve stimulation (ONS) has been studied for various chronic headache disorders, including chronic migraine and cluster headaches, with some evidence supporting its efficacy.