Sometimes our bodies are just primed for an episode or a flare-up.
We don't always realize that we're already sitting at, let's say, 70% on our way to flaring, so even the smallest trigger will induce a full blown episode.
For instance, my husband has environmental allergies. Dust and pollen are the worst, but a ton of fragrances and scents really bother him, so we keep fragrances in the house to a minimum. Now, normally, the scent of vanilla is fine. However, if he's been around flowers or has dusted the house, even the smell of vanilla will send him sneezing with nose tingles and itchy eyes. Not because vanilla is awful for him, but that he was primed for a severe reaction even if the trigger is minute.
I find that the same principle applies with SO many of my illnesses.
If my swelling disease isn't well controlled, something as small as getting flustered in traffic could cause significant swelling. If I've accidentally pissed off my intestines, it doesn't matter how safe the foods are that I eat, anything I eat for the next week will worsen the flare.
So if I'm already exhausted - if I have already pushed myself too hard - any little trigger might cause a major disruption. The trick is to figure out what it feels like when you're primed to worsen and then take the time to let it settle back down to a manageable level - be that inflammation, pain, energy, etc...
So sometimes, I'll actually be feeling okay, but I will take the day to be a 'puddle', which can feel wrong if you've grown up with the mindset that you need to constantly be productive. On these particular puddle days, my only job is to rest; to lie in bed, watch tv or listen to audiobooks, nap if I need to, curl up with blankets and become a puddle on the bed. That way, I can avoid the severe and painful flare-up that forces me to stay in bed for multiple days in a row.
Puddle days are when I feel okay but know that I need to rest.