When you know that someone was unwell previously, and you haven't talked to them, or heard about them since the time you knew they were unwell.

Thanks both of you!

I agree with Marilyn that it's not that common, but I wouldn't go as far as saying that it's unnatural. I would say it's possibly more formal, and not as caring as Marilyn's alternatives.

This expression does not sound very natural to me. If I knew that someone was previously sick or somehow unwell, I would say "I hope you're feeling better now" or "I hope things are better now" or "I hope you are better now" depending on the situation. .