Yeah, you might not feel up to something if you're feeling tired.

是啊，如果你感觉得累了，你可能会觉得不想去做某事。

If we don't feel up to something then we don't have the strength and energy to do it.

如果我们觉得不能胜任某件事，那我们就没有力量和精力去做这件事。

We have to feel up to something, like feel up to going to the gym or feel up to going back to work after a vacation.

我们得在 feel up to 后加东西，比如可以去健身房，或者度假后觉得可以回去工作。