Answer:
withdrawal symptoms
Explanation:
When one person consumes a substance (such as alcohol, drugs or caffeine) in a regular basis, their body adjusts to this substance and when they stop taking it, they have unpleasant physical and mental effects because they already had the habit of consuming the substance. This effects are called withdrawal symptoms.
In the question, your mother has a daily cup of coffee and she even has more cups of coffee through a day. When she misses her daily doses of caffeine she gets an unpleasant symptom which would be the headache. Therefore, this is an example of withdrawal symptoms.