Hello. Thanks for asking from HCM. I can understand your concern. Diarrhoea in your mother could be due to drug reaction, food poisoning or food allergy. Head injury directly does not cause diarrhoea. You should check what medication she was given or taking at present. Find out if she is taking any antibiotic, because penicillins or erythromycin can cause diarrhoea. Food allergy can be suspected if she had abdominal cramps along with diarrhoea after taking specific food item. Symptoms will resolve after avoiding food. Food poisoning symptoms include fever, abdominal pain, diarrhoea, vomiting. It usually subsides on its own in 3-5 days. You should take plenty of fluids like water, lemon water, juice. For pain, you can take painkiller like Diclofenac sodium after proper prescription. You can correlate her features and reach unto some conclusion. If symptoms still persist, you can consult physician. Avoid fatty and spicy food. Thanks. Hope it will help you. Take care.