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uk Health & medical scares severe cramps after vomiting • weakness after diarrhoea • cannot keep fluids down • can’t rehydrate after sickness • dehydration from vomiting • dehydration from diarrhoea • severe dehydration warning signs • dizziness and weakness after gastroenteritis • muscle cramps dehydration salts • shaky weak after stomach bug • vomiting and diarrhoea dehydration • dark urine not peeing much • fainting after vomiting • oral rehydration sachets • rapid heartbeat dehydration • confused after vomiting • older adult dehydration risk • pregnancy dehydration vomiting • diabetes sick day dehydration • severe thirst and weakness

What to do if…
you develop severe cramps and weakness after vomiting or diarrhea and cannot rehydrate well

Short answer

Treat this as potentially urgent dehydration/electrolyte loss. If you cannot keep fluids down or you’re very weak, faint, confused, or passing very little urine, get urgent help via NHS 111 (or 999 in an emergency).

Do not do these things

  • Do not “push through” severe weakness/cramps and try to sleep it off if you cannot rehydrate.
  • Do not chug large amounts quickly (it can trigger more vomiting and won’t replace salts well).
  • Do not drink alcohol.
  • Do not drink fruit juice or fizzy drinks while you’re having diarrhoea/vomiting (they can make diarrhoea worse).
  • Do not take anti-inflammatory painkillers like ibuprofen while you’re dehydrated, unless a clinician has specifically told you to (if you take regular medicines, ask for “sick day” advice rather than guessing).
  • Do not take medicine to stop diarrhoea if you have blood in your poo, a high fever, severe belly pain, or you feel very unwell—get advice instead.
  • Do not drive yourself to get help if you feel faint, confused, very weak, or you’ve nearly collapsed.

What to do now

  1. Check for emergency red flags (act immediately). Call 999 if:
    • you collapse, cannot stay awake, are confused, or have a seizure
    • you have severe shortness of breath or chest pain
    • you have severe/worsening abdominal pain (especially in one spot) or a rigid belly
    • you vomit blood (or “coffee grounds”), or have black/tarry poo, or significant rectal bleeding
  2. If you can’t rehydrate well, get urgent NHS advice now.
    • If your GP practice is open and you can contact them safely, request urgent advice.
    • If your GP is closed, or you can’t get through, call NHS 111 and say: “vomiting/diarrhoea, severe cramps and weakness, struggling to keep fluids down.”
  3. Start “tiny sips + salts” rehydration while you’re arranging help.
    • Use oral rehydration solution (ORS) sachets mixed exactly as the packet says (a pharmacist can help you choose one).
    • If vomiting: take very small sips/teaspoons frequently. If that stays down for 15–20 minutes, slowly increase.
    • If you can’t tolerate ORS yet: take small sips of water or diluted squash until you can get ORS in.
  4. Reduce ongoing losses and strain.
    • Rest, keep cool, and avoid exertion.
    • Eat only if you feel able; choose bland foods (toast, plain rice, crackers, bananas). Food is optional—fluids come first.
  5. Do two “getting worse” checks (and escalate if they worsen).
    • Urine: very dark, or hardly any for many hours.
    • Standing: you feel faint or your vision “greys out” when you stand. If either is worsening, re-contact 111 promptly (or 999 if severe).
  6. If you’re higher risk, say so early. Tell 111/your GP if you are pregnant, over 65, immunosuppressed, have kidney disease, have diabetes, or recently took antibiotics or travelled—this can change how urgently you’re assessed.

What can wait

  • You do not need to figure out the exact cause right now (virus/food poisoning/etc.).
  • You do not need to force normal meals—rehydration is the priority.
  • You do not need to decide about work/school/travel today.
  • You do not need to try multiple over-the-counter medicines while you’re unstable—get advice first.

Important reassurance

Severe cramps and weakness after vomiting/diarrhoea can happen when your body is short of fluid and salts, and it can feel suddenly frightening. Getting urgent advice and rehydrating in small, steady amounts is a sensible, protective response.

Scope note

These are first steps only. If symptoms persist, recur, or you have medical conditions/medications that raise risk during dehydration, you may need clinician review even if you start to improve.

Important note

This is general information, not a diagnosis. If symptoms are severe, rapidly worsening, or you cannot keep fluids down, use NHS 111/999 for urgent assessment.

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