Okay, the following is what I want to say. But it is too long. So I want to find a better way to express it (the bold), using some idioms or short phrases.
Your friend caught a cold. So he took medicine. A week later he got better. He says he got recovered because he took medicine. However, I want to tell him that the cold went away not because he took medicine, but because it has run its course.
I asked people around and someone said that I can express it like "You got better because it is time you recovered" (It is + past tense). Is this the right expression? Or is there another way to express it?