Oftentimes, when we have problems on our minds, we may find it hard to fall asleep at night, as our brains process and think and generally worry. When this happens, we say that we’re losing sleep over something.
However, if someone mentions a problem and you are not at all worried about it, you can express that idea saying, “I’m not losing any sleep over it.”
A: I’m worried about our situation in the company.
B: I’m not losing any sleep over it. They may threaten a lot, but they can’t fire us—they need us!
Be careful with this one, it can be a bit sarcastic.