expression
don't overwork yourself; don't overdo it; take it easy
A gentle, caring expression used to tell someone not to push themselves too hard, physically or mentally. Often said to someone who is working too much, studying too hard, or trying to do something beyond their limits.
See also: 無理 (むり)
最近残業が多いみたいだけど、無理しないでね。
It seems like you've been working a lot of overtime lately; don't overdo it, okay?
風邪が治ったばかりだから、無理しないでゆっくり休んで。
You just got over a cold, so take it easy and rest up.
Formed from 無理 (むり, 'unreasonable, impossible') + しないで (negative て-form of する, 'do'), literally 'without doing the unreasonable'. The phrase is a fixed expression meaning 'don't overdo it'.