Go Downhill:

If things are “Going Downhill”, it means that they are getting worse and worse.

I used to be good at basketball when I was in high school, but my abilities started going downhill after I turned 40.

She was really attractive when she was young but her looks have been going downhill lately.

I think I will need glasses soon.  My eyesight seems to be going downhill fast.

Persian: بدتر شدن