As expatriates are not usually covered by state health insurance, you can visit a public hospital but will have to pay for the treatment. For an additional fee you can even get an individual room. However, be aware that public hospitals are usually poorly equipped and overcrowded; hence most expatriates opt for treatment in a private hospital.
Thai hospitals
There is no such thing as “free treatment” in Thai hospitals. Before any treatment, you will have to show that you have acceptable insurance or money to pay your hospital stay, otherwise hospitals might not admit you for in-patient care. Foreign health insurance is usually accepted in Thailand, although it depends upon your insurance company. If your insurance company has a bad history of paying bills, then your treatment may be refused.