It seems to me that there are a number of English verbs that can stand for acts that can be done voluntarily or involuntarily. Sometimes we can't help but laugh, but anyone with even mild acting talent can laugh deliberately. Sometimes our coughs are involuntary, but anyone can cough deliberately. The arrival of a meteorite isn't controlled by an agent, but in what sense do workers arrive on time to their jobs without arriving deliberately?
Which brings us to the question: Can some verbs be unergative in some contexts and unaccusative in others? Or am I missing something?