"Down to the wire" refers to a situation where precision and accuracy are most needed, such as in a baseball game where the bases are loaded, there's a full count, and this hit means winning the game. My example is complicated but I hope it helps. =)
Currently, You can't lie down in a ROBLOX game unless the creator added some way for you to do it (By either a tool, GUI, or some other means). There is no universal button or key that you can press that will let you do it in any game you want.