Sleeping in a train is usual thing in Japan.

It is not surprise that taking 1 hour to commute in Japan.
It is hard to get up early if you are lack of sleep but many people sleep in a train while commuting.

It is not safe in other country but it is not rare thing in Japan. Many people have experienced going past their stop once with sleeping too deeply.
With comfortable rhythm of the train, we cannot stop falling in sleep.

It is not so safe to sleep in late time such as after 10pm with drinking, some pickpocket might around you.