Signs You Might Be Low on Electrolytes, and When It Is a GP Matter

The signs people search for, tiredness, headache, cramp, dizziness and brain fog, are the signs of a hundred things, from thirst to a missed meal or a short night. A measurably low sodium, potassium or magnesium has its own shape: low sodium brings nausea, headache, confusion and unsteadiness, and in older adults it is often a medicine rather than sweat; low potassium brings weakness, cramps, constipation and palpitations; low magnesium brings twitching, tremor, tiredness and loss of appetite. None can be judged from symptoms alone, all are diagnosed by a blood test, and none is self-treated with a sachet.^{1-3, 14} It is the symptoms spoke of the Wellgard electrolytes guide.

Sources checked on 30 October 2026.

What are the signs of low electrolytes?

The "five symptoms of electrolyte imbalance" lists online are broad; the clinical versions are narrower. The European guideline defines hyponatraemia as a blood sodium below 135 mmol/L (mild 130 to 135, moderate 125 to 129, profound below 125) and grades the symptoms: nausea without vomiting, confusion and headache are moderately severe; vomiting, abnormal drowsiness, seizures and coma are severe.¹ Low potassium, below 3.5 mmol/L, often causes no symptoms until it falls below about 3.0; then weakness, leg cramps and constipation, and as it falls further, rhythm disturbance.² Low magnesium shows as muscle twitches, tremor, tiredness and loss of appetite;¹⁴ the signs of low magnesium has the detail. The early items overlap with poor sleep, low iron and stress; your medicines, a recent illness and recent sweating are better clues.

Are you dehydrated or low on electrolytes?

Dehydration is a water deficit (creatine does not cause one: does creatine dehydrate you); the NHS signs are thirst, dark strong-smelling urine, passing urine less often, headache, light-headedness, tiredness and a dry mouth.⁴ Sweat is more dilute than blood: in 506 athletes whole-body sweat sodium averaged about 36 mmol/L, while blood sodium counts as low below 135, so sweating loses proportionally more water than salt.^{1, 5} Low sodium in exercisers comes from the other direction: at the 2002 Boston Marathon 13% of finishers tested were hyponatraemic, and gaining weight during the race, from drinking more than they lost, was an independent risk factor alongside a finish over four hours.⁶ Electrolytes for runners does the sweat arithmetic by distance. After a stomach bug the NHS answer is an oral rehydration solution from a pharmacist.⁴

What depletes electrolytes, and which medicines are involved?

Outside illness and sweat a common cause is a prescription; the last row covers the diseases asked about.

Which organ is most sensitive to electrolyte imbalance?

The heart and the brain. Potassium sets the electrical rhythm of heart muscle, so low and high potassium both produce palpitations and dangerous rhythms.^{2, 10} Sodium governs the water content of brain cells: when it falls fast the brain swells, the cause of the confusion, drowsiness and seizures, and correcting it too quickly damages the brain a second way, so hospitals raise sodium at a controlled rate over days.^{1, 8} So raising a low sodium quickly is a clinician's job, not a home task.

Can you check your electrolyte levels at home?

Not usefully. No home device reads blood sodium, potassium or magnesium. The NHS test is the urea and electrolytes panel, U&E, which checks whether the amount of certain substances in your blood may be causing your symptoms; a GP orders it when symptoms sit beside a risk such as a water tablet, an antidepressant, kidney disease or older age.^{8-10, 15} Magnesium is a separate test, which the MHRA advises doctors to consider before and during long-term acid-suppressant treatment.¹⁴ The one home measure concerns sweat: whole-body sweat sodium in athletes ranged from 18 to 71 mmol/L, and the runners page's weigh-before-and-after method turns your own sweat rate into a number.⁵ A craving for salt alongside exhaustion and weight loss is one of the Addison's signs in the table.¹¹

When is it a GP, 111 or 999 matter?

A GP appointment for tiredness, cramps, twitching, palpitations or constipation that persist, particularly if you take a water tablet, antidepressant or acid suppressant, have kidney disease or started a new medicine recently; ask whether a U&E and magnesium are due. NHS 111 or an urgent GP appointment if you or a child are unusually tired or drowsy, dizzy on standing in a way that does not pass, passing dark urine or much less of it, breathing fast or with a fast heart rate, if fluids will not stay down, or for any child under five with signs of dehydration.^{4, 16} 999 for blue, grey, pale or blotchy skin or lips, skin that feels cold, difficulty breathing, confusion, being much sleepier than normal or hard to wake, a seizure or loss of consciousness, or the heatstroke signs of a very high temperature with hot skin that has stopped sweating.^{4, 7}

How much sodium is in an electrolyte drink, and is that a lot?

UK electrolyte sachets run from about 300 mg of sodium (0.75 g of salt) to nearly 2 g (close to 5 g of salt), against the NHS adult maximum of 6 g of salt a day; do you need to drink electrolytes every day sets each sachet against that line.¹² A high-sodium sachet replaces sodium after hours of heavy sweating; on a desk day it adds to the salt already in food, and in the Cochrane review's trials in white participants, cutting sodium lowered systolic pressure by about 1 mmHg with normal blood pressure and about 6 mmHg with hypertension.¹³ With high blood pressure, heart failure or kidney disease, ask a pharmacist first.

What we don't know

• How often antidepressants lower sodium: reported rates for SSRIs run from 0.06% to 40% because the studies differ in design and cut-offs.⁹
• Why only some people on a thiazide are affected: the mechanism is incompletely understood.⁸
• How large the acid-suppressant risk is: the 1.4-fold figure pools nine observational studies, and the MHRA says the exact incidence is unknown.^{3, 14}

Frequently asked questions

What are the first signs of low electrolytes?

For sodium, nausea, headache and a muddled or unsteady feeling; for potassium, weakness and cramps; for magnesium, twitching and tremor.^{1, 2, 14}

How do you feel when your sodium is low?

Sick, headachy, tired and confused, with unsteadiness and falls in older adults; in severe or sudden cases, drowsiness and seizures. It is diagnosed by a blood test, not by how you feel.^{1, 8}

What is the fastest way to replenish electrolytes?

After sweating, a drink and a salted meal; after vomiting or diarrhoea, rehydration sachets in small frequent sips; for a low level found on a blood test, whatever the clinician treating the cause prescribes.^{1, 4}

What are the symptoms of low electrolytes in the elderly?

Confusion, unsteadiness, falls, nausea and tiredness, most often from low sodium on a thiazide water tablet or an antidepressant, sometimes years into treatment; a new muddle in an older person is a GP visit and a blood test, never a sachet.^{8, 9}

Sources

1. Spasovski G, et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. European Journal of Endocrinology, 2014. Clinical practice guideline of three European societies; non-government research support. PubMed 24569125.
2. Kardalas E, et al. Hypokalemia: a clinical update. Endocrine Connections, 2018. Narrative review; no specific funding. PubMed 29540487.
3. Cheungpasitporn W, et al. Proton pump inhibitors linked to hypomagnesemia. Renal Failure, 2015. Meta-analysis, 9 observational studies, 109,798 patients; funding not stated. PubMed 26108134.
4. NHS. Dehydration. Page last reviewed 1 May 2026. nhs.uk.
5. Baker LB, et al. Normative data for regional sweat sodium concentration and whole-body sweating rate in athletes. Journal of Sports Sciences, 2016. Retrospective analysis of athlete testing, 506 athletes; authors employed by a sports-drink maker's research institute. PubMed 26070030.
6. Almond CS, et al. Hyponatremia among runners in the Boston Marathon. New England Journal of Medicine, 2005. Prospective cohort study, 488 runners; NIH-funded. PubMed 15829535.
7. NHS. Heat exhaustion and heatstroke. Page last reviewed 28 May 2026. nhs.uk.
8. Filippone EJ, et al. Thiazide-associated hyponatremia. American Journal of Kidney Diseases, 2020. Narrative review; funding not stated on PubMed. PubMed 31606239.
9. De Picker L, et al. Antidepressants and the risk of hyponatremia: a class-by-class review. Psychosomatics, 2014. Literature review, 21 studies and over 100 case reports; funding not stated on PubMed. PubMed 25262043.
10. Sarnowski A, et al. Hyperkalemia in chronic kidney disease: links, risks and management. International Journal of Nephrology and Renovascular Disease, 2022. Narrative review; one author declares drug-industry grants and fees. PubMed 35942480.
11. NHS. Addison's disease. Page last reviewed 19 September 2025. nhs.uk.
12. NHS. Salt in your diet. Page last reviewed 17 April 2023 (review overdue). nhs.uk.
13. Graudal NA, et al. Effects of low sodium diet versus high sodium diet on blood pressure. Cochrane Reviews, 2020. Systematic review of randomised trials, 195 included references; authors at public institutions, no industry funding. PubMed 33314019.
14. MHRA. Proton pump inhibitors in long-term use: reports of hypomagnesaemia. Drug Safety Update, 11 December 2014. gov.uk.
15. NHS. Blood tests. Page last reviewed 2 November 2023. nhs.uk.
16. NHS. Diarrhoea and vomiting. Page last reviewed 21 December 2023. nhs.uk.

Spotted something out of date? Email support@wellgard.co.uk with the page address and the sentence.

This article is general information, not medical advice. A low sodium, potassium or magnesium is diagnosed by a blood test and treated by the clinician who finds the cause; never stop or change a prescribed medicine, and never try to correct a diagnosed imbalance with salt or sachets at home.