大丈夫じゃないのに無理をしていたら、周りも出来ると判断してしまう。
出来ないことは出来ないとはっきり断って出来る人にお願いすること。

Clearly say no
If you are forcing yourself to do something that is not okay, people around you will assume that you can do it. Clearly refuse to do what you cannot do and ask someone who can do it to do it for you.