The short answer
Under Sl. No. 74 of Notification No. 12/2017-Central Tax (Rate), dated 28 June 2017, health care services by a clinical establishment, an authorised medical practitioner or para-medics are exempt from central tax, at a nil rate. The notification is published by the Central Board of Indirect Taxes and Customs (link under References).
What counts as health care services
The notification defines health care services as any service by way of diagnosis or treatment or care for illness, injury, deformity, abnormality or pregnancy in any recognised system of medicines in India, and includes transporting the patient to and from a clinical establishment. In plain terms: consultation, examination, procedures and treatment by a clinic or a medical practitioner are what the exemption is about.
What the definition leaves out
The definition does not include hair transplant or cosmetic or plastic surgery, except when it is undertaken to restore or reconstruct anatomy or functions of the body affected by congenital defects, developmental abnormalities, injury or trauma. A clinic that offers cosmetic procedures should not assume they are exempt.
Things a clinic sells that are not health care services
The exemption covers health care services. A clinic may also sell goods, such as medicines or products. Those are a different kind of supply, and how they are taxed is a question for your accountant, who can also tell you whether you need to register.
How Yuktii treats invoices
In Yuktii, an invoice whose every line is linked to a treatment is shown as GST (Exempt) with no tax charged. Any other invoice, including one for a consultation fee alone or a mix of items, applies the tax rate set for the clinic, which the clinic can set to zero. The clinic's GST number is stored on the clinic record. Yuktii does not split tax into CGST, SGST and IGST and does not print HSN or SAC codes, and it does not decide whether something is taxable; that is for the clinic and its accountant.
Keep the record either way
Whether an invoice carries tax or not, keep an invoice per visit with the patient, the service, the amount and the payment. Yuktii links invoices to treatments and tracks payments and pending balances, so the record is there when the accountant asks.
Check the current notification
The notification linked below is the original of 28 June 2017. Tax notifications are amended, so check the current position with the Central Board of Indirect Taxes and Customs or your chartered accountant before you decide how to invoice.