Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Go to an emergency department promptly if you have repeated vomiting, cramping abdominal pain, increasing abdominal swelling, or difficulty passing gas or stool.
Call emergency services if symptoms include severe or constant abdominal pain, fainting, confusion, marked weakness, trouble breathing, or signs of shock such as cold clammy skin.
Fever with worsening abdominal pain or a very tender, rigid abdomen also needs emergency care.
Do not wait for symptoms to become severe.
Do not eat, take laxatives, or attempt to manage a suspected obstruction at home while waiting for assessment.
If you have recently been treated, seek urgent reassessment if pain, swelling, vomiting, fever, or inability to pass gas returns.
And for anyone, someone who:
Arrange routine follow-up for wound concerns that are not rapidly worsening, persistent changes in appetite or bowel habits, questions about diet, or management of the condition that caused the blockage.
Every sign above is quoted from the sofidex article on Small bowel obstruction. If you are not sure, err upward — it is always reasonable to be checked.