hello sir, first of all primidone is an anti seizure medication. you should be sure that you are suffering from a seizure disorder before starting this drug.as you said you also have COPD and if you are using inhaler drugs for COPD symptoms (beta agonists like albuteral, salbutamol) , they have a side effect of causing tremors. so make sure it s not tremors and it s a seizure disorder. then coming to primidone it s known to cause vertigo and ataxia even sedation sometimes. that s why it s not much preferred by most of the clinicians nowadays ( as the are much better drugs like carbamazepine and more are available now). primidone will not cause any breathing problems. it s too exhaustive if I start explaining the mechanism behind these side effects. but I will try to give you a brief idea. the reason why people suffer from seizures is due to hyperexcitability of their nervous system. so these drugs are used to suppress this hyperexcitability and sometimes it causes suppression of normal excitations which leads to side effects like sedation , vertigo and gait disturbances which actually depends on nervous system excitations. so modern drugs are developed which are more specific for these hyperexcitability neuron pathways and not affiliated affecting the normal ones. hope this information helps you.