It's a pretty general thing to say. There might be better phrases for the specific situation you're in, but I could only think of one that is as general and could be used in any situation you could say "sorry to spring this on you": Sorry to surprise you like this.

Sorry to unload this out on you like this, unexpectedly.

What a very peculiar expression! If someone said that to me, I would be quite alarmed.

I wouldn't!

I'd think about "sorry to spread this on you"