Chia seeds are not for everyone, every time. If your diarrhea is from a bacterial infection (think food poisoning with a fever), fiber might trap the toxins inside you. That’s bad. You want that stuff out.
Also, if you have IBS or Crohn's disease, your gut might hate chia seeds. The high fiber can be a trigger. Listen to your body. If it says "no," trust it. There’s no medal for being a chia martyr.
And please, don’t use chia seeds as your only treatment. If diarrhea lasts more than two days, or you see blood? Call a doctor. Don’t be a hero with a bag of seeds. Seriously.