Hi and welcome to just answer.
This sounds like one or more of the air bags has let go and there may also be a problem with the compressor if it's been working overtime trying to keep up, either way it needs checking out properly as you may save the compressor if it's still ok.
The airbags are a common thing to let go and when one goes the others usually follow. Replacing all the bags and compressor is expensive but there is a conversion kit available which reverts back to normal springs and another that replaces the compressor to use airline connections if you're on a budget.
I hope this helps