If you’re anything like me, you’ve probably had mornings where you wake up to that strange tingling sensation in your arms, hands, or fingers — like part of your body forgot how to feel. It’s that familiar “pins and needles” feeling, where everything goes a little numb for a few moments, then slowly returns to normal as if waking up along with the rest of you.

So what exactly is going on when that happens?

This prickly, sometimes mildly burning sensation is known medically as paresthesia. According to the National Institute of Neurological Disorders and Stroke, paresthesia is a sensation that isn’t painful, but definitely uncomfortable. It often shows up out of nowhere and can affect areas like your hands, feet, arms, or legs.

The most common version is what happens when you’ve been lying in a certain position too long — maybe your arm tucked under your pillow or your leg bent under the other. That temporary numbness is called transient paresthesia. It’s typically the result of putting prolonged pressure on a nerve, cutting off normal circulation.

Luckily, in most cases, the solution is simple. To get feeling back in the limb, you just need to get blood flowing again. Stretching the area, changing position, or giving it a gentle massage usually does the trick in a minute or two.

But while most episodes are harmless and short-lived, paresthesia can sometimes be a sign of something more serious. Chronic paresthesia — where the tingling doesn’t go away or keeps returning — may stem from underlying issues such as nerve damage, a herniated disc, or even neurological conditions like multiple sclerosis or stroke. In more rare cases, it might be caused by tumors or vascular injuries.

So when should you take it more seriously?

You should talk to a doctor if the tingling comes on suddenly, especially after a head injury, or if it affects an entire arm or leg. Other red flags include weakness or paralysis, trouble speaking, dizziness, or a sudden, severe headache. Likewise, if it develops slowly over time, affects both sides of the body, comes and goes unpredictably, or is tied to certain repetitive movements (like typing), it’s worth getting checked.

Even if it’s just affecting your toes or fingers, frequent paresthesia could be your body waving a small red flag.

It should go without saying that readers should see a doctor or qualified medical professional if they are concerned. It may be time to seek help if your paresthesia:

Begins suddenly
It follows a recent head injury
Involves an entire arm or leg
You experience weakness or paralysis
You experience confusion
You experience difficulty talking
You experience dizziness
You have a sudden, severe headache
You have had a head injury
Your doctor suspects or needs to rule out a brain tumor or stroke
It begins or worsens gradually
It affects both sides of the body
It comes and goes
It seems related to certain activities, particularly repetitive motions
It affects only a part of a limb, such as your toes or fingers
Have you ever experienced paresthesia? Let us know in the comments.