Please seek urgent medical help if you experience severe or persistent abdominal pain, severe vomiting, signs of dehydration, symptoms of a serious allergic reaction, or a sudden loss of vision (including partial loss) - sudden, painless vision loss, usually in one eye, can be a sign of NAION, a very rare eye condition, and should be assessed urgently at eye casualty or A&E.
You should also seek urgent medical attention if you experience any symptoms that feel serious or are rapidly getting worse.