Stop coughing at night

I had a bad cough last month and so was my mum. I cannot take cough medicines as i was on medication for kidney disease and taking other meds not prescribed by a nephro is prohibited. I was searching for natural remedies. I found a post in fb about putting a slice of potato on my feet then cover them with socks overnight. It did not work for me.(Maybe because i am on medication?)But it actually worked with my mum.She did not have any cough the whole night and had a really good night sleep. The potatoes turned really black in the morning. We tried it again on the next night.Again it did not work for me but worked for my mum. She had a good night sleep.