A mock zombie apocalypse sweeping the nation has people on the run for their lives.

About an hour and a half into my first day undead, I start to realize that the afterlife as a freshly minted zombie is more challenging than I first assumed it would be. First, there’s the brutal Florida sun slowly frying my carefully cultivated pallor as I crouch on a hill in an off-road park outside of Orlando. And there’s all the red goop and mud covering me from head to toe. It pools on the brim of my neon visor and drips off, slowly bakes into my hair, then crusts and flakes off. Then, of course, there are the living. The fittest survivors crest the hill in batches, unbowed by a few miles of muddy obstacles.

It’s my job to follow them, running them down on their homestretch to safety. As a chaser zombie, I sprint after these humans — and fast. I growl. They shriek. I catch the unlucky ones. Frankly, it gets exhausting.

But as tiring as it is, I begin to understand the rush described by the veteran zombie friends I’ve made. And, of course, I know this is all make-believe — just another hour and a half and I’ll score a shower, a medal and a cold draft beer.

As both a horror-movie fan and an on-and-off runner, I’ve enlisted as a volunteer zombie in the Clermont, Fla., edition of Run For Your Lives. The 5k-race series wisely combines two white-hot trends in pop culture: adventure-themed obstacle courses and a craze for ­everything zombie.

Runners traverse a course that’s a little longer than three miles (and which is dotted perilously with mud pits, rope climbs and mazes) and, along the way, evade volunteer zombies. These zombies, in turn, are trained to go not for brains but for the runners’ clip-on flag belts. If the runners make it through the race with at least one flag, they “live.” Let the zombies snatch them all, and they’re toast. (At least figuratively; everyone is allowed to finish the race.)

The first Run For Your Lives event hit the woods of Maryland — outside Baltimore, where the organization is based — in 2011, drawing some 12,000 participants and spectators. Since then, the series has spread across the country like, appropriately, a virus, with some 22 races planned for 2013 and less-organized imitators scrambling in its wake. The average run participants are, for the most part, what you’d expect: ranging from morbidly curious power walkers to überfast CrossFitters with sinewy pecs and shaved heads. The zombies, though, represent a different breed — a spirited one, one happy to escape into fantasy and possessing a special brand of humor.

“You have to have the spirit that you’re kind of an actor and this is your role to play,” says Ashley Watson, a 27-year-old from ­Baltimore who, over the course of a year, channeled her inner zombie for two races in her own city, as well as one in Boston. “You get into the mindset of growling and not talking or really chasing people and acting like you’re really hungry.”