The most common and most likely answer to this crossword clue is the 5 letter word SKIED
S
K
I
E
D
Buddy explains!

The straight part
We know that "Went downhill, perhaps" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case went downhill, perhaps = skied.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SKIED mean?
SKIED verb- To move on skis
- To travel over (a slope etc.) on skis; to travel on skis at (a place), (especially as a sport)
- To hit, kick or throw (a ball) extremely high.
- To clear (a hurdle, high jump bar, etc.) by a large margin.
- To hang (a picture on exhibition) near the top of a wall, where it cannot be well seen.
- To drink something from a container without one's lips touching the container.