A wave of dizziness washes over you, leaving you wobbly and weak. Or you’re suddenly lightheaded and grab the furniture to stay upright. Many of us experience moments of dizziness, but when is it time to see a doctor — or even call 911?

First, quick clarification: People often use the terms “dizziness,” “lightheadedness” and “vertigo” interchangeably, but they are different things, said Dr. Joseph Chipman, a Novant Health neurologist. Vertigo is the sensation that your surroundings are spinning or that you’re moving when you’re not.

One of the most common causes of vertigo is benign paroxysmal positional vertigo, which occurs when calcium carbonate crystals normally in the inner ear get dislodged.

Vestibular migraines also can cause vertigo, and people can have such a migraine without a headache. Both conditions need the attention of a doctor but are not typically emergencies.

Lightheadedness is different, often feeling like a “head rush,” resulting in dizziness. Chipman and Dr. Kaustubh Dabhadkar, a Novant Health cardiologist, explained what causes this kind of dizziness, when it’s not a big deal and when you need medical help right away.

Here’s when dizziness is an emergency.

If you feel dizzy and you have not changed your position — such as from sitting to standing — that may be a medical emergency involving your heart.

“If it’s a new onset and you don’t have good reason and your heart rate is too fast, call 911. Don’t try to drive,” Dabhadkar said. “If you are lightheaded and we don’t have a good explanation and it’s a new sign, you call 911.”

In such cases, you could have a narrowed or leaky heart valve, or atrial fibrillation (AFib), where the heart beats out of rhythm. You also could be having a heart attack — even if you have no other symptoms.

Stroke could be another cause of dizziness that doesn’t change with your body’s position.

“Sometimes you can have a stroke that doesn’t affect one side or your speech. It’s not the most common type of stroke (but) it could be all of a sudden, you feel dizziness and you aren’t changing positions,” Chipman said.

Lightheadedness also can accompany traditional signs of stroke — and a blood clot in the lungs also can produce that feeling, Dabhadkar said. Any of these issues are immediate emergencies.

The bottom line for dizziness that’s serious and warrants an ER visit: "If someone is having constant dizziness and it’s not fluctuating based on sitting or standing, that is an emergency,” Chipman said.

Here are other causes for dizziness that may not mean a trip to the ER — but which do mean you need to see a doctor.

Possible dizziness cause: Medications

Medications that affect the brain’s neurotransmitters can cause dizziness, including drugs for seizures, neuropathic pain and antidepressants. Chipman usually tells his patients that if they start a medicine and begin feeling dizzy, to give it five days. If the feeling persists, it’s time to get seen and discuss stopping the medication.

Medicines that lower blood pressure are another culprit, said Dabhadkar. Sometimes this is why you’re taking the medicine — such as lisinopril for high blood pressure — but they may be doing their job too well. Drugs for other conditions can change your heart rate. For example, prostate-health drug Flomax affects blood pressure and heart rate and can make you feel dizzy.

And guess what? If you take a GLP-1 for weight loss, that also could cause dizziness.

“The common situation that we are seeing is patients taking GLP-1 drugs to lose weight and they’re still taking their blood pressure medicine,” Dabhadkar said. “I’m seeing a lot of patients with low blood pressure.”

It’s crucial for people taking GLP-1s to monitor their blood pressure, he said, and consult with their physician about whether other medications should be stopped and if their food and water intake is sufficient.

Possible cause for dizziness: Changing position

“One thing we don’t typically get overly concerned about are vagal episodes: Standing for a long time, where blood pools in the legs. Or a sudden change of position,” Chipman said. Dizziness that comes from standing up suddenly or dehydration or hunger typically aren’t emergencies.

But even if your dizziness is not urgent, there’s one important caveat: Dizziness of this sort may not be a medical emergency. But falling is. Falls are the leading injury-related cause of death in people 65 and older and the death rate is going up. If you experience dizziness that leads to falls, you need to see a doctor, Dabhadkar said.