On a slippery slope

If someone or something is on a slippery slope, it's in a situation which is getting worse and will continue to get much worse. Sometimes we say it's 'going downhill'.

Examples:

The country's economy was on a slippery slope following the closure of its biggest industry.

With his big drinking problem he was on a slippery slope to bad health. 

Take note

If someone is described as beingas slippery as an eel, it means they are not honest and you can't trust them. It is difficult to catch them behaving in this way.