What's The Difference Between Brain Fog And Just Being Very Tired? We Asked An Expert & Here's What They Said

Andrew Zaeh/Bustle

Some days, you can pour coffee into your face for hours without achieving noticeable results. Your brain feels congealed, as if suspended in a skull-ful of jello, and your thoughts get stuck in the gelatinous mass such that you cannot say or type anything coherent. Everything is accomplished in excruciatingly slow motion (if at all), your mind moving at the pace of an old PC. Your memory is a sieve. Your eyes are coated in fuzz. You need a nap. You need 10 naps. Moving through the world feels like wading through molasses. Everything is hard and also dumb. You could be very very tired, yes, but this feels somehow more severe. It feels like a woolly fog rolled into your head and colonized your brain space.

"Certainly, the term 'brain fog' is not something definitive in standard medicine," David Perlmutter, M.D., a neurologist based in Naples, Florida, tells Bustle. "Nevertheless, most people fully understand that there are times when it is difficult to think clearly." Those moments may strike occasionally, or they may be all-the-time occurrences. Regardless, Perlmutter says, the calling card reads the same way.

"We know that when people complain of brain fog they indicate that there thinking process is slow, they may have difficulty multitasking, may be easily distracted from a task, or may even be temporarily forgetful," he says. Another common complaint? Fatigue. Which is to say, you might have brain fog because you're very tired.

Certain medical conditions — multiple sclerosis, celiac disease (post-gluten consumption), chronic fatigue symptom, lupus, lyme disease, low thyroid, imbalanced blood sugar, adrenal insufficiency, chronic pulmonary problems — sometimes come with the aforementioned brain fog feels. For a number of uterus-havers, brain fog also sets in a particular moments in the menstrual cycle. (Some call this "period brain," i.e., the frustrating phenomenon of feeling extreme mental fuzziness on and around your period.)

Some people also experience brain fog when they fail to get the sleep they need, itself a subjective equation because "there is no magic number with respect to the amount of sleep an individual should get as everyone is different," Perlmutter says. Age plays a role, as do your own personal dietary and exercise patterns. For people 18 to 64, the Sleep Foundation recommends between seven and nine hours. What's crucial to feeling with it the next day, Perlmutter says, is sleeping through that entire window.

"Some individuals feel that they are getting eight hours of sleep each night but in reality, their sleep may be interrupted by such things as restless legs, sleep apnea (temporarily stopping breathing), or other problems," he says. "The important point is that these individuals may not fully awaken and therefore they may not be aware of the fact that their sleep is interrupted and as such, non-restorative."

A lack of sleep, or a lack of quality sleep, features prominently among brain fog's most common causes. Other culprits, Perlmutter notes, include medications — for pain, anxiety, blood pressure — alongside caffeine. On the previously mentioned subject of mainlining coffee, Perlmutter says that too much caffeine can make a person feel fuzzy and weird, or impede their sleep that night. Drinking alcohol can also leave a person mentally in the weeds the next day: If you want to avoid brain fog, Perlmutter says, maybe keep it to two glasses of wine. Additionally, Perlmutter recommends exercise: Not only is it thought to improve brain health and function, it also helps people sleep better and longer.

But how do you know whether you have brain fog or are just very tired? "Individuals who experience fatigue generally complaining of simply feeling tired all the time," Perlmutter says. Often, he adds, "they also notice that their brains just don't seem to be working up to speed, as is typically described with individuals who state that they have brain fog."

Being very tired might leave you feeling foggy, but so might any of the other usual suspects previously noted. To determine which one is to blame, get your sleep cycle in check and see if the fog burns off. Or keep track of your lifestyle habits and research the prescription drugs you may be taking: If you always feel totally unable to think clearly, it's probably time you got your butt to a doctor's office.