Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Severe pain, heavy bleeding, fainting, confusion, or a swollen rigid abdomen require emergency evaluation.
New fever, increasing bleeding, worsening pain, frequent vomiting, or signs of dehydration deserve prompt contact with a healthcare professional.
Follow-up should focus on both symptoms and control of inflammation.
Feeling better does not always mean the colon has fully healed.
Routine follow-up is appropriate for stable symptoms, medication monitoring, nutrition concerns, or planning surveillance tests.
The article also says
A clinician may monitor bowel frequency, bleeding, weight, blood counts, iron levels, inflammatory markers, or fecal calprotectin.
Repeat colonoscopy may be recommended to check healing, clarify a diagnosis, remove polyps, or watch for precancerous changes in people with long-standing ulcerative colitis.
People taking immune-modifying treatment may need laboratory monitoring and infection-prevention planning.
Vaccination needs should be reviewed before or during treatment because some therapies reduce immune defenses.
Any decision to change or stop treatment should be made with the prescribing clinician.
Every sign above is quoted from the sofidex article on Colitis. If you are not sure, err upward — it is always reasonable to be checked.