Went downhill (4)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">went downhill</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Another definition for worsened that I've seen is " Deteriorated".)
(Other definitions for slid that I've seen before include "Moved (eg, on ice)" , "Skidded, slewed" , "Moved smoothly along a surface" , "Slipped" .)