In the days after Halloween, the haze starts to fade for employees of HalloweenCostumes.com and they can start catching up on missed sleep.

Most of the work at the Mankato company — one of the nation’s top sellers of costumes — is geared toward preparing for the crush of orders in September and October.

Those are the months when the family-owned business feels like a multinational giant, said Chief Executive Tom Fallenstein. Staffing jumps from several dozen to more than 1,000 as hundreds of seasonal workers arrive to fill orders that accelerate as Halloween gets closer.

Then it all ends, almost in an instant. And like farmers after harvest or political campaigners after Election Day, the company’s executives and staffers start to relax and reflect on just-completed business.

“We think of all the things we want to improve for next year or the new designs we want to work on,” Fallenstein said after the holiday this week. “But right now, most of us are thinking we’ll start that next week.”

HalloweenCostumes.com gets 80 percent of its annual revenue during September and October, with 50 percent coming in a three-week period. Many staffers work 12-hour days and seven-day weeks during that period.

“We’re trying to get all the shipments out, make everyone happy,” Fallenstein said. “You forget what day it is, when you went to bed or whether you said something yesterday or last week.”

The business grew out of his mother’s love of making costumes for Fallenstein and his three sisters. Two sisters began renting out some of the spare costumes more than 20 years ago. Fallenstein in 2001 started selling costumes online, and the family brought all the businesses together in 2005.

Today, their operation has grown to include an online gift site called Fun.com and a T-shirt site called Shirts.com. But HalloweenCostumes.com is the biggest — and due to its seasonality, the most challenging.

“For a few weeks, we get to be a half-billion dollar company and then we’re back to a small company,” Fallenstein said. “You get to experience what that’s like and create an infrastructure to support that.”

During that concentrated period of taking and shipping customer orders, staffers always learn something new. “Every department has takeaways every year on either software, systems or processes we know we can improve,” he said.

And the pressure is on, even more intensely than other retailers experience during the year-end holiday season. “You can’t have a bad day in October. Otherwise, you have a bad year,” Fallenstein said.

This year, company planners recognized that with a movie about Wonder Woman coming out during the summer, costumes of the superhero would be in high demand, and they ordered plenty. They missed out on the holdover desire for costumes of characters from Disney’s “Descendants” movie, which came out two years ago, and the craze for costumes related to the horror movie “It.”

“You hope [a costume] is going to be as big as you think. Sometimes it’s not, sometimes it is,” Fallenstein said. “That’s an issue we face every year.”

Most of the second-guessing and reassessment will happen later. On Wednesday, the day after Halloween, the company started promoting Santa and other holiday-related costumes on its website.

Meanwhile, there’s also the company’s own Halloween party to prepare for, expected to draw 2,000 people to a Mankato ballroom this weekend, including all of its regular and seasonal staff.

“It’s kind of like our Christmas party, but everyone will dress up,” Fallenstein said. “You’ll see some unique costumes, which might even inspire some costumes we make for next year.”