Completely normal sentence! It basically means "relax." Person A is saying to Person B to relax, because working every day is unhealthy. "Unplug" means to take a break from electronic devices (e.g., work email, phone, etc.) and "unwind" just means relax from a stressful situation.

Yes, it a very normal sentence. When we say "unplug and unwind", it is just a fun way of saying relax. When you "unplug" you are switching off from all the things that might be causing you stress, like work or study. "Unwind" means that you are releasing any tension that you might have that has caused you to become uptight, or wound up. Hope that helps! :)