Laughing hard

I'm curious about the origin and more elaborate meaning of the adjective "hard" as used in expressions like:

laugh hard
sleep hard
think hard

Etymology: Middle English, from Old English heard; akin to Old High German hart hard, Greek kratos strength

In your usage it is an adverb.

Main Entry: hard

Date: before 12th century
1 a : with great or utmost effort or energy : STRENUOUSLY b : in a violent manner : FIERCELY c : to the full extent -- usually used in nautical directions d : to an immoderate degree e : in a searching, close, or concentrated manner
2 a : in such a manner as to cause hardship, difficulty, or pain b : with rancor, bitterness, or grief
3 : in a firm manner : TIGHTLY
4 : to the point of hardness
5 : close in time or space