Your GHIC/EHIC lets you get medically necessary healthcare that cannot reasonably wait until you come back to the UK. Whether treatment is necessary is decided by the healthcare provider in the country you're visiting.
Medically necessary healthcare includes things like treatment for a long-term or pre-existing medical condition and routine medical care for pre-existing conditions that need monitoring.
The GHIC/EHIC card can be used when visiting an EU country, including Switzerland.