Coughing at night can arise out of a number of causes.
Many of these are minor health conditions, including a slight allergy to house dust or inflammation in the nasal passages causing mucus to drip down into the back of the throat.
However, there are some causes such as asthma, or for someone a bit older with heart problems, heart failure which requires medical attention.
For more information, you might wish to read our page on causes of coughs at night.
As you will see, the range of possibilities is rather large and to really get to the bottom of this, you should make an appointment with your doctor.