I have windows 8 on a HP Laptop. When I close the lid while downloading "peer to peer" the speed decreases dramatically.
The laptop is not sleeping nor hibernating (I disabled those options), and the hard disk remains active.
I found the answer in the forum below solved this problem for me. As I understand it, closing the lid changes the antennae angle (because they are in the lid), thereby affecting the ability to receive the wifi signal.
In short the solution is to close the lid then prop the computer vertically (hinge down) by leaning it against a wall or other item. Seems odd, but has worked for me.