The answer to the question is not clear from the search results. There are conflicting results, and some of them are not reliable sources. Some sources suggest that it is possible to travel in a sleeper coach with a general ticket without any penalty, while others mention a penalty for travelling without a ticket. One source suggests that if seats are empty, there is no penalty, but if not, the penalty must be paid. However, it is important to note that travelling without a valid ticket is illegal and can result in fines and imprisonment. It is always recommended to purchase a valid ticket before boarding a train to avoid any legal consequences.