From the Wikipedia page on “slave ship”:Often the ships, also known as Guineamen, transported hundreds of slaves, who were chained tightly to plank beds. For example, the slave ship Henrietta Marie carried about 200 slaves on the long Middle Passage. They were confined to cargo holds with each slave chained with little room to move.
Slaves were forced to lay face down with their arms by their side and their wrist chained to their waist. Some were even stacked on top of each other with no room to move. Keep in mind there were not any restrooms and they were exposed to bodily fluids, etc. Not many of the slaves survived, many dying from dehydration and disease.