Short answer

• If you vomit after finishing your ekashna (one‑sitting meal) or beyashna (two‑sitting meals), the meal you took is counted. Do not eat again that day; otherwise the niyam (vow) is broken.
• If vomiting happens during the same sitting before you have concluded it, you may complete that same sitting only if your health allows. If not, stop.
• If there is genuine medical need (illness, weakness, medicine), you may respectfully change or end the niyam with proper pachchakhan (taking permission/exception), then take what is necessary. Later do pratikraman/alochana and resume from the next day.

Notes in simple Jain terms

• The vow is about “number of sittings.” Vomiting does not create a new sitting or allow an extra one by itself.
• Health is also ahimsa. If needed, take roga‑agar (exception due to illness) properly, without stubbornness, and with remorse.
• Prayashchitta: If you had to eat again without taking pachchakhan, accept it as niyam‑bhanga in pratikraman that evening and take a fresh pachchakhan for the next day.

Tradition points

• Both Shwetambar and Digambar maryada accept illness‑based exceptions. Wordings and time‑windows can differ; follow your guru/sangh’s pachchakhan format.

Practical tips to avoid recurrence

• Eat lightly, calmly, and within the vowed time window.
• Prefer simple, easily digestible items; avoid excess quantity and heavy/fried foods.
• Sip boiled/filtered water as permitted by your niyam.

For a quick refresher on types of fasts and niyams, see this overview: