Leslie : I'm not sick, I just have allergies, OK? I took a Claritin, and i threw that up, so I took another one, I threw that up, and then I took a third and it stayed down. I'm getting better.

I've already written about " one false move " episodes, in which a small decision or action has regrettable consequences. But while just about anyone would feel stupid for sticking one's head where it doesn't belong , people react to sickness in all kinds of different ways. Some of us feel guilty for neglecting our health (or touching a door handle in a rest room), some feel a kind of relief at having an excuse to slack off, and some just refuse to acknowledge being sick.

Sitcom characters can't get drunk or high every week, and that's why we have the flu episode. Slurred speech, wobbly legs, hallucinations, sudden stupidity... the flu comes with every comic trick short of putting a man in a dress. (Though "Flu Season" gives us Rob Lowe in a hospital johnny, which is a different kind of pleasure.) Parks and Recreation checks off all the symptoms of a flu episode, but it ends with a curve that establishes Leslie Knope as a super-achiever.

Welcome to the “100 Best Sitcom Episodes of All Time,” a countdown for 2012. Each episode will get a separate blog post, counting backward toward No. 1. A list of the programs revealed so far is here (and on Pinterest ), and an introduction to the project is here .

When Parks and Recreation premiered, city bureaucrat Leslie Knope (Amy Poehler) seemed to be a female version of The Office's Michael Scott: enthusiastic but incompetent, gregarious but unable to read social cues. The one difference from the start was that Leslie was not lazy, and as the show found its footing, her absurdly ramped-up work ethic became her defining trait. She's now closer to The Dick Van Dyke Show's Rob Petrie, who was also obviously very good at his job, to the point of doubting that any one else was up to his standards. And, like Rob Petrie, she's funniest when her high energy and intelligence fuel some kind of obsession.

Andy: Leslie, I typed your symptoms into the computer, and it says you might have "network connectivity problems."

In "Flu Season," Leslie is trying to revive the annual Harvest Festival in Pawnee (the show's fictional Indiana city), and her success depends on a presentation to the local Chamber of Commerce — or the "Chamber of Secrets," as fevered Leslie calls it, which sounds awesome. Even when she's admitted to the hospital with a 104-degree temperature by "the most beautiful nurse in the world" (Ann Perkins!), she's determined to make that presentation.

Leslie: Can I get some money for the cab that I took over here, please?

Ben: Sure, how much?

Leslie: I'm not sure. I looked at the meter and it had Egyptian hieroglyphs on it. Do you know the exchange rate?

The flu has also hit sulky April (Aubrey Plaza), who uses her hospital stay to torment her nemesis, Ann (Rashida Jones); and Chris (Rob Lowe), who is not kidding when he says, "My body is finely tuned like a microchip and the flu is like a grain of salt, it could literally shut down the entire system."

Leslie's new love interest, former "boy mayor" Ben Wyatt (Adam Scott), insists that she's too sick to give a speech, but nothing can stop her. And after laughing at Amy Poehler's "sick" slapstick, I got a little teary-eyed at Ben's awed reaction to what happens when Leslie finally gets to the podium.

• In the A.V. Club review of this episode the night it aired, Steve Heisler could tell it was a turning point:

Though the show introduced the characters of Ben and Chris with a big splash (name-brand actors will have that effect), I also felt like "The Flu" gave them a chance to feel like they belong in Pawnee. First, Ben sees Leslie deliver a stellar speech despite being riddled with sickness and acknowledges that Leslie Knope is truly a special gal—one worthy of chicken soup. Chris, meanwhile, has one of his rare bouts of sickness ("Stop. Pooping.") and emerges with a fresh outlook on the comfort of Pawnee, an excitement for Ann, and a motivation to invent a flimsy excuse to stay around.

• I've repeated many times my preference for sitcom episodes that commit to one story, but I like that "Flu Season" doesn't take the obvious route of giving everyone a turn to be sick. Leslie's nominal supervisor, the mighty Ron Swanson (Nick Offerman), instead gets a funny storyline about bonding with Andy (Chris Pratt) and discovering the virtues of burritos ("a whole new meat delivery system"). This is also a pivotal episode for Ron in that he tentatively starts to take some interest in the personal lives of his colleagues.

Ron: The less I know about other people's affairs, the happier I am. I'm not interested in caring about people. I once worked with a guy for three years and never learned his name. Best friend I ever had. We still never talk sometimes.

• Another Parks and Recreation episode, "Fancy Party," is at No. 12.