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What to do if…
your blood sugar reading is suddenly very high and you feel sick

Short answer

Treat this as urgent: check ketones (if you can) and contact medical help now. If you have signs of DKA/HHS or you’re getting worse, call 911 or go to the ER immediately.

Do not do these things

Do not try to “work it off” with exercise when you feel sick or ketones might be present.
Do not take a new/guessed extra insulin dose if you don’t have a clinician-provided correction/sick-day plan.
Do not stop insulin (especially long-acting/basal) unless a clinician specifically tells you to.
Do not ignore vomiting, severe drowsiness/confusion, or deep/rapid breathing.
Do not drive yourself to urgent care if you feel weak, confused, very sleepy, or your vision is blurred.
Do not rely on a CGM reading alone if it doesn’t match how you feel—confirm with a fingerstick.
If you take an SGLT2 inhibitor and you have possible ketoacidosis symptoms (nausea/vomiting, abdominal pain, trouble breathing, unusual sleepiness), do not “wait it out” at home.

What to do now

Check for “call 911 now” red flags. Call 911 (or go to the ER) if any of these apply:
- You have repeated vomiting, severe belly pain, deep/rapid breathing, fruity breath, confusion, extreme sleepiness, fainting, or signs of severe dehydration.
- You have ketones and you feel very unwell, or you cannot test ketones and you’re getting worse.
Re-test to confirm it’s real. Wash and dry hands and re-check with a fresh strip. If you use a CGM, confirm with a fingerstick.
Test for ketones as soon as possible.
- If you’re sick and your blood glucose is 240 mg/dL or higher (or your plan says to), test urine or blood ketones.
- If ketones are present and you feel sick, contact your clinician/on-call service right away. If you feel very sick, are vomiting, or symptoms are worsening, go to the ER.
If you do not have a clear sick-day/correction plan, don’t improvise.
- Call your diabetes clinician/on-call line (or your primary care office) now and tell them: your glucose, ketone result (if you have one), and symptoms.
- If you can’t reach anyone promptly and you’re very high + sick, choose the ER rather than routine urgent care.
Follow your personal sick-day/correction plan (exactly) if you have one.
- Take diabetes medications/insulin as prescribed, including clinician-written sick-day instructions.
- If you use an insulin pump and this is unusual: check the infusion site/tubing and confirm insulin delivery, then follow your pump sick-day instructions. If you suspect delivery failure and you’re worsening, seek urgent care guidance immediately.
Start steady fluids. Sip water or other sugar-free fluids. If you can’t keep fluids down or vomiting continues, seek urgent care (dehydration can worsen quickly).
If you take an SGLT2 inhibitor and you have ketoacidosis-type symptoms, treat it as urgent.
- Many US labels advise stopping the SGLT2 inhibitor and seeking medical attention immediately if ketoacidosis symptoms occur (especially nausea/vomiting, abdominal pain, trouble breathing, unusual fatigue/sleepiness). The safest route is usually the ER if symptoms are significant.
Write down essentials for clinicians. Time-stamped glucose and ketone results, any fever/illness symptoms, vomiting/diarrhea, and what meds/insulin you took.
Don’t stay alone if you’re worsening. Ask someone to stay with you or check in frequently. If you need emergency care, bring your meds/devices and testing supplies if safe.

What can wait

You do not need to figure out the exact cause right now. Safety and assessment come first.
You do not need to make long-term medication changes today.
You do not need to “tough it out” or keep normal plans—resting and monitoring is enough until you’re stable and advised.

Important reassurance

It’s understandable to feel alarmed: high blood sugar plus feeling sick is a meaningful warning sign. Checking ketones and getting help early is the safest move and often prevents things from escalating.

Scope note

These are immediate first steps only. Follow-up care (adjusting meds, checking for infection, reviewing pump settings, etc.) should be done with your diabetes clinician.

Important note

This is general information, not medical advice. Very high blood sugar with illness can become a medical emergency (including DKA or hyperosmolar hyperglycemic state). If you’re unsure, pregnant, on an SGLT2 inhibitor, can’t test ketones, or symptoms are worsening, err on the side of urgent ER evaluation.

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What to do if…your blood sugar reading is suddenly very high and you feel sick