(TNS) — Just one semi-clear nostril would do. The bar is that low.

After a day with not-so-terrible cold symptoms, it’s alarming, frustrating and confusing — and maybe other reactions that involve expletives — to suddenly have every upper airway avenue stuffed tight with swelling and congestion simply because the sun went down.

There’s a cough — even if you didn’t sputter once during the day — a consequence of the mucus escaping down the throat.

Fever and chills may also make their debut.

As you toss and turn, stack pillows and fluctuate between four blankets and nudity, there’s an internal debate: “Are these symptoms really worse at night, is there something especially wrong with me, or is it all in my head?”

The answers are yes, no and no.

“People are not out of their minds. These symptoms are worse at night,” said Tom Walsh, Allegheny Health Network infectious disease physician and medical director of the system’s antibiotic stewardship program. “It’s been studied, and there are a lot of potential mechanisms for why this occurs.”

The first reason is something like boredom. The litany of daytime distractions are suddenly missing. No one is calling your name. There’s no task list. It’s just you and too much time and attention to focus on your (relative) misery.

The other factor is gravity.

“When you’re upright, a lot of that nasal congestion will drip forward,” said Amanda Hercules-Smith, internal medicine physician and medical director of St. Clair Health urgent care. “But when you’re laying flat, you get that postnasal drip, mucus being accumulated at the back of the throat and triggering a cough response.”

The back-of-the-throat mucus build-up is the reason you might clear your throat endlessly upon waking and feel the need to blow, literally, through a box of Kleenex.

Those issues aside, there’s a formidable foe during the evening hours that sends immune systems into overdrive. And while it can feel as though that force is designed to crush your dreams of a good night’s sleep, it’s an act of tough love by the king of nighttime sickness slaying, your circadian rhythm.

That system — which also orchestrates sleep/wake patterns, hormone releases and more — governs patterns of the immune system, largely with cortisol, a stress hormone.

“Any insult to your body — trauma, a viral infection — your brain senses that as a stressor,” Hercules-Smith said.

In response to that stress, a beyond-typical amount of cortisol is released in its telltale pattern: higher amounts during the day and less at night.

“The lower cortisol levels — at night — cause a heightened immune response,” she said.

That accounts for the higher body temperature at night, and the increased swelling and mucus in the airway as immune cells rush toward compromised areas.

“These inflammatory responses are the ways the body fights pathogens,” Walsh said. “Before the antibiotic era, it’s not as though everyone died. That’s because the immune system is a wonderful thing, and able to accomplish great things on its own. It may make us feel crummy, but it’s doing its job and actually helping us,” which may be the last thing anyone suffering through an upper respiratory infection wants to hear while lying awake at 3 a.m.

Practically, here’s what to do.

Fight postnasal drip by declaring gravity as your pal and sleeping on an incline.

Drink plenty of fluids. “It decreases the thickness of mucus, but also helps you, over time, to fight that fever and lower your core body temperature,” Hercules-Smith said.

Consider a (recently cleaned) humidifier to moisten the air and calm the airway.

Take an over-the-counter antihistamine or cough suppressant with intention. Walsh recommends researching when your chosen medication reaches peak effects, and matching that point with when you hope to nod off.

And perhaps just as helpful as any of these tips is the anxiety-relieving, science-backed knowledge that uncomfortable nights while fighting a viral illness aren’t hallucinations, but are par for the snotty course.

“It’s really a complex interplay between all of these pathways that are active during the night and upon awakening,” Walsh said. “You’re not having worsening of the virus itself at that time. You’re actually having symptoms of your body’s inflammatory response, fighting the pathogen. That’s what you’re really feeling, and that’s an important difference.”

(Abby Mackey is a registered nurse and can be reached at amackey@post-gazette.com and IG @abbymackeywrites)