Travellers to Indonesia need to arrange comprehensive travel insurance before visiting the country, because there is no reciprocal healthcare agreement in place between the UK and the country.
Hospitals in the main tourist areas of Indonesia are of a high standard, and can treat most conditions, although for severe medical problems you may require medical extraction back to the UK or to Singapore.
Malaria and Dengue Fever are a problem throughout the country, and you should consult a doctor prior to travel in order to arrange appropriate protection.