When all my limbs went numb one morning, I went to urgent care in a panic. It turned out to be a vitamin B12 deficiency.

The author, Kelly Rissman. Courtesy Kelly Rissman When I experienced unexplained pins and needles and weakness in all my limbs, I started to panic. About a week later, I went to the doctor and found out I had a severe vitamin B12 deficiency.

  Here’s what a B12 deficiency can look like, plus treatment, as well as how I’m feeling today. On a Wednesday morning in May, I went for my regular run around lower Manhattan. I enjoyed the breezy weather, ate my usual meals, and went to work.

Then, as I was settling in for the night, something unusual happened. I was lying on my right side in bed when pins and needles radiated through my left arm. I wasn’t putting pressure on my left arm, so why was it asleep? I shook it out and contorted my body, trying to stretch my limb to rid myself of the feeling but felt no relief.

Then my left hand went numb. After 30 minutes of panic, I convinced myself it was all in my head and eventually fell asleep. By the time I woke up in the morning, the same tingling sensation had spread to both arms, hands, legs, and feet.

I was really freaking out. I was panicked and looking for answersI hobbled over to a nearby urgent-care center, where the doctor told me the tingling could be explained by a viral infection, even though she didn’t run any tests or give me any prescriptions. I left feeling even more hopeless than when I had stumbled in — and more tingly.

With no change in my symptoms, I saw my internist, who promptly conducted an extensive blood-work panel. As I waited five days for results, I became so weak that it was debilitating; I couldn’t even take a lap around my block.  Finally, the panel came back: I had a severe vitamin B12 deficiency.

What it’s like to have a severe vitamin B12 deficiencyAccording to Dr. Edwin Serrano, a neurology resident physician at MedStar Georgetown University Hospital, a B12 levels of about 300 picograms per milliliter is considered normal, and below 200 pg/ml is considered low. Mine was hovering around 175 pg/ml.

My numbers probably didn’t plummet this low overnight.  “Typically, symptoms occur after vitamin B12 deficiency has been untreated for years,” said Dr. Brad Kamitaki, an assistant professor of neurology at Rutgers Robert Wood Johnson Medical School.

Many people are initially asymptomatic. He added that B12 deficiency “can be undiagnosed or underdiagnosed since symptoms can be nonspecific,” like cognitive slowing, fatigue, tongue swelling, arm or leg tingling, and difficulty walking. B12 deficiency typically has two causes: malabsorption or inadequate intake.

Some conditions, like atrophic gastritis or celiac disease, can block the absorption of B12, while vegan and vegetarian diets can lead to insufficient intake, as animal products are a main source of B12. Symptoms did not go away immediately once I started treatmentAt least the treatment sounded easy: vitamin B12 injections for a month, then daily supplements. I figured my symptoms would vanish after a week of shots — I was wrong.

Your body takes awhile to replenish its B12, Serrano said: “If there are neurological symptoms, these can linger between three months to one year. ” That was the case for me. Even though I was getting treatment, my symptoms worsened before they improved — and the way my symptoms affected my life cannot be overstated.

Leg numbness persisted. I also found myself without an appetite and regularly skipped meals. My brain fog was overwhelming.

Headaches became so excruciating I could no longer sleep. My vision became blurry. Alarmed, my doctor thought the two latter symptoms warranted an MRI brain scan to rule out a tumor or multiple sclerosis; a neurologist later told me B12 deficiency explained both.

It’s important to note there are some folks who may be more at risk of a vitamin B12 deficiency than others, including those on plant-based diets, Kamitaki said. “I’d also want people to be aware that adequate vitamin B12 intake is essential during pregnancy and if exclusively breastfeeding, as effects of vitamin B12 deficiency in the developing fetus and infant can be significant,” Kamitaki said. Serrano added that older populations were also at higher risk, as cases of B12 deficiency increase with age.

I was extremely lucky that I acted as quickly as I did. Serrano said that if symptoms went untreated, it could cause “irreversible damage” to the nervous system and lead to the inability to walk as normal, permanent muscle tightness, and loss of motor function in your legs. He added that untreated symptoms could alter the ability to produce red blood cells, which increases risk of heart failure, and may even increase a person’s risk of dementia.

 Nearly five months after my initial panic in May, my symptoms have virtually disappeared. My strength and energy have returned, my brain fog has lifted, my numbness has subsided, and I’m able to take my morning run again. Read the original article on Insider.