The verb prostrate means to lie face-downward in submission or despair. More generally, it means to make helpless or defenseless. Illness, injury, grief, despair — any of these things can prostrate someone.
The word prostrate traces back to the Latin word prostratus, meaning “thrown down.” If you are prostrate, you feel thrown down and laid flat. It can describe lying on the ground in a helpless position, or it can be used to describe someone who has been overcome or made unable to function, such as someone who is prostrated by grief or illness.