I agree. We really wouldn't say "I rest after effort" in English. It sounds terribly awkward! This sentence should be changed. If my students wrote this on an essay in my class, I would definitely make them correct it and explain themselves in another way.
'I rest after effort' and 'I am resting after effort' are simple sentences, but they sound odd. I think it's because 'effort' is so vague; normally, you would say more specifically what you had been doing.