A lurker asked me to answer this so I will make an exception
It is national law that a health care professional MUST treat a victim in danger until such timr the victim is considered STABILIZED upon which the victim can be transported or rendered to facilities for continuing care.
IMSS is a three part government, employer, member subscription HMO. Seguro Popular is a less sophisticated member direct HMO and ISSSTE is an HMO for civil servants.
Health care is not free in Mexico. Only first aid services to stabilize the patient. Continuing care can be expensive as hell or less expensive third-world grade of sophistication.
Hospitalized without membership means a patient is responsible for any and all orally delivered medication which they must seek and pay for at a private farmacia. Medicines injected are given by the hospital and are charged on your bill.
Patients are accompanied by a policeman wearing a pistol to the business office upon discharge where they must satisfy 100% of the hospital charges before exiting the hospital. This is standard operating procedure all over the country.
This info is derived from multiple personal experiences including an 11-day stay in Seguro Popular involving major surgery.