Feeling dizzy and weak suddenly is often caused by low blood pressure on standing, dehydration, low blood sugar, an infection or a medicine side effect. It can also be a sign of a heart rhythm problem, a heart attack or a stroke. Call 911 if it comes with chest pain, fainting, a very fast or slow pulse, or face drooping, arm weakness or slurred speech.
Medically reviewed by
Board-certified cardiologist · Katy & Sugar Land, TX
Fellowship-trained in cardiovascular disease, interventional cardiology, echocardiography and advanced heart failure and transplant cardiology. Former Assistant Professor of Cardiology at McGovern Medical School.
Why do I feel dizzy and weak suddenly?
Dizziness and weakness usually mean the brain and muscles are briefly not getting enough blood flow, oxygen or fuel. The most common causes are temporary, but several are emergencies.
| Cause | Clues | Urgency |
|---|---|---|
| Stroke | Face drooping, arm or leg weakness on one side, slurred speech, vision loss, sudden severe headache | Call 911 |
| Heart attack | Chest pressure, breathlessness, cold sweat, nausea | Call 911 |
| Heart rhythm problem | Racing, pounding, skipping or very slow heartbeat; fainting | 911 if fainting or ongoing |
| Low blood pressure on standing | Dizzy when getting up, improves lying down | See a doctor |
| Dehydration or heat | Thirst, dark urine, recent heat, vomiting or diarrhea | Fluids; urgent if confused or fainting |
| Low blood sugar | Shaky, sweaty, hungry; diabetes medicines | Treat now; 911 if confused |
| Anemia | Gradual fatigue, pale skin, breathless with activity | See a doctor soon |
| Medicine side effect | New or changed blood pressure, heart, sleep or pain medicines | Call your doctor |
| Inner ear problem (vertigo) | Room spinning, worse with head movement | See a doctor |
- Face drooping, weakness or numbness on one side, slurred speech or vision loss
- Chest pain or pressure, or shortness of breath
- Fainting, or a very fast, very slow or irregular heartbeat
- Confusion, a sudden severe headache or trouble walking
Heart causes of sudden dizziness and weakness
Arrhythmias. A heart that beats too slowly (bradycardia), too fast (tachycardia or SVT) or irregularly (atrial fibrillation) can drop blood flow to the brain, causing lightheadedness, weakness and fainting. According to the NHLBI, arrhythmias can cause dizziness, fainting and fatigue.
Heart attack. Weakness and lightheadedness can accompany a heart attack, sometimes with only mild chest discomfort.
Valve disease and heart failure. A narrowed aortic valve or a weak heart may not increase output enough during activity, causing dizziness or fainting with exertion.
Stroke warning signs: BE FAST
Sudden dizziness with weakness can be a stroke, especially when weakness is on one side. Remember BE FAST: Balance loss, Eyes (vision loss), Face drooping, Arm weakness, Speech difficulty, Time to call 911. MedlinePlus notes that stroke treatment works best when started quickly. Atrial fibrillation is a major cause of stroke; learn about post-stroke cardiac care.
Low blood pressure, dehydration and medicines
Orthostatic hypotension is a drop in blood pressure when you stand up. It is more common in older adults, with dehydration, after prolonged bed rest and with blood pressure, prostate or water pills. Hot Texas weather makes it worse. Read about low blood pressure, POTS and dehydration and dizziness. Never stop a prescribed medicine on your own; ask your doctor whether a dose change is appropriate.
What to do when you feel suddenly dizzy and weak
- Sit or lie down right away to avoid falling; raise your legs if you feel faint.
- Check for stroke signs (BE FAST) and call 911 if any are present.
- If you have diabetes and a meter, check your blood sugar.
- Sip water if you may be dehydrated and can swallow safely.
- Check your pulse if you can; note whether it is very fast, slow or irregular.
- Call 911 for any warning sign below, or if symptoms do not quickly improve.
How doctors find the cause
Evaluation may include blood pressure lying and standing, an EKG, blood tests for blood count, sugar, electrolytes and thyroid, an echocardiogram, and heart rhythm monitoring with a Holter, event monitor or mobile cardiac telemetry. For infrequent episodes, a long-term implantable rhythm recorder may be considered.
Dizziness and fainting evaluation in Katy and Sugar Land
If dizzy spells keep coming back, Advanced Cardiology can look for heart rhythm, blood pressure and valve causes. Dr. Khalid sees patients at our Katy and Sugar Land offices, where EKG and echocardiogram testing are available and heart monitors can be started. Learn about our dizziness and fainting care.
Katy office: 410 W Grand Pkwy S, Suite 4D, Katy, TX 77494
Sugar Land office: 7102 Tarrington Ave, Suite 505, Sugar Land, TX 77479
Phone: (713) 258-6111
We also see patients from Fulshear, Richmond, Rosenberg, Stafford, Missouri City and west Houston.
Recurring dizzy spells or near-fainting?
A heart rhythm monitor can often find the cause. Request a cardiology visit in Katy or Sugar Land.
Having symptoms right now? Call 911. Do not wait for an appointment.
Frequently asked questions
Why do I suddenly feel dizzy and weak?
Common causes include low blood pressure when standing, dehydration, low blood sugar, infections and medicine side effects. Serious causes include heart rhythm problems, heart attack and stroke.
Can heart problems cause dizziness and weakness?
Yes. Arrhythmias, heart attacks, valve disease and heart failure can reduce blood flow to the brain and muscles, causing dizziness, weakness and fainting.
When is sudden dizziness an emergency?
Call 911 if dizziness comes with one-sided weakness, facial drooping, slurred speech, vision loss, chest pain, breathlessness, fainting or a very fast or slow heartbeat.
Can dehydration make you dizzy and weak?
Yes. Dehydration lowers blood volume and blood pressure, which can cause dizziness and weakness, especially when standing or in hot weather.
What tests check for heart causes of dizziness?
An EKG, echocardiogram, blood tests and heart rhythm monitoring such as a Holter or event monitor are common first steps.
Should I see a cardiologist for dizziness?
See a cardiologist if dizziness comes with palpitations, chest discomfort, fainting, exertion, or if you have known heart disease.
Trusted health resources
- Dizziness, MedlinePlus Medical Encyclopedia
- Stroke, MedlinePlus, U.S. National Library of Medicine
- Arrhythmias, National Heart, Lung, and Blood Institute (NIH)
- Fainting (Syncope), MedlinePlus, U.S. National Library of Medicine
- Low Blood Pressure, MedlinePlus, U.S. National Library of Medicine
Medical disclaimer: This article is for general education and is not a diagnosis or a substitute for care from your own doctor. If you think you may be having a heart attack, stroke or another emergency, call 911 right away.
