Collapse, fall, etc. in a heap
Definition 1 of 2
Pro Tip 1/3Physical Exhaustion
Used when someone is so tired they become physically unable to stand or remain conscious. 
He had been awake for 36 hours and finally collapsed in a heap on the couch.
Pro Tip 2/3Dramatic Imagery
Creates a strong visual of someone falling dramatically, emphasizing the suddenness of their collapse. 
As the referee blew the final whistle, the player collapsed in a heap, utterly defeated.
Pro Tip 3/3Emotional Impact
Can depict a strong emotional response leading to a physical reaction, like overwhelming joy or relief. 
She received the news of her acceptance and collapsed in a heap, crying tears of joy.