Runner duckling health question

One of my month-old runners is suddenly having trouble holding its head up, I think. It walks a little bit sideways, like it gets tired of supporting the weight of its head, and when it sleeps, it lets its head lay forward on the ground instead of folding it back to rest on its chest like all the others. Is this something I should be worried about?

Some questions that will help figure out what's going on...

What do you feed them? Do you add Niacin via supplements or Brewer's yeast?
What type of bedding do you use? Please describe their environment.
Can you share pics or a video of the duckling exhibiting this behavior?
Does the duckling eat, drink & poo with no issues?

I'll tag some more knowledgeable members and they'll probably have more questions.

@casportpony
@jtn42248
@Miss Lydia
@needlessjunk
@Amiga
@WVduckchick
@caesargirl

Do they free range explain your set up, could she have eaten anything toxic rotting vegetation, stagnant water? botulism can cause limber neck. If you suspect Botulism there is a thread in the stickys about flushes. I'll get it for you.

https://www.backyardchickens.com/t/700526/flushes-for-aiding-in-toxin-removal#post_9508213

My thoughts - nutritional sensitivity (needs more niacin), toxin, infection, intestinal blockage (do you see the little eating, pooping?)

Debs Flock and Miss Lydia make good points. I cannot be near the computer much tonight, just wanted to let you know.

What is the brooder temperature, have there been children or other pets around the ducklings?

What is their water setup? They need water with food 24/7, and a head washer - see the sticky on raising ducklings -

Can you post a picture of it's poop?

-Kathy

Unfortunately I don't have a picture of Zuko's poop :/ but I don't see anything unusual in their habitat, and it seems to be eating and drinking as vigorously as ever (it actually seems fatter than all the rest today...). Right now I've got it and its 7 siblings in a 4'x4' inflatable pool with white wood shaving bedding everywhere but around the water, which has a ring of wood pellets to soak up mess, all of which gets replaced daily. Water gets changed/refilled at least 3 times a day, and 3 or 4 times a week I take them outside to play in a pond liner half full of fresh water so they can splash and swim, but it has platforms along the side so they can stand if they want to. They eat Purina Flock Raiser with brewers yeast and a little bit of chick grit, which is replaced daily, and lots of koi pellets for treats. They have a brooding light at night, but it's been 80-90° during the day so they have a heatless sun lamp during the day. They don't have a head washer, though, I'll definitely get something set up for them tomorrow.

I think it might be doing better now, like maybe it was fatigued or maybe overheated and just needed a good rest? There were a lot of people going in and out of the garage all weekend and I know they were doing their best not to disturb the peepers, but I worry they didn't get enough sleep. I may have just been overreacting... these are my first ducklings and I'm just so worried about them

[VIDEO]
Here's a video of them from today (we were celebrating their one month birthday with crickets). Zuko is the fat black one that's running around.

Looking pretty good from what I see

They all look great, the lil blk one laying down didn't seem to interested or maybe just not hungry they are all so pretty.

Oh thank goodness! Yeah, Azula (the little black one in the back) isn't as snack-motivated as everyone else, and it was pretty late, so I think she just wanted to sleep. She'd have gotten up for koi pellets, though!