The longitudinal berths in the sleeper buses make it extremly unsafe for passengers in case of accidents especially head on collisions.
The spine of the victim lying in longitudinal position in the bus is at significant risk of severe injury due to axial compression from the impact of a head on collision.

It is compounded by the fact that the body of the victim will be thrown against the hard barrier that seperate front or the back berth during a head on collision further increasing the severity of the injury. There are no seat belt like restraints in the sleeper berths.
The configuration of berths make evacuation of victims that much more difficult in comparison to a sittings bus.

Safety wise it is much better to travel by a semirecliner sitting bus rather than a sleeper bus.