There are several approaches in your situation and they aren't mutually exclusive. They all boil down to accepting where you at and they require you to know where you want to go.
Accepting where you're at
You know your condition, that's a given. But what does that mean in context with the world?
My favorite metaphor is a treasure map. You know you stand between a certain rock and an oddly shaped cactus. But what does that mean for the map? Are there more places like this or is where you are completely unique?
You suddenly can become sick beyond working capability, but isn't that true for your colleagues, too? Sure, your condition is unique from the inside and please do not take this as belittling it. From the outside though, you're sick at home unable to work. There are a lot of rock-cactus-formations like that on the map.
I recognize that your condition is of chronic nature and you may be on sick leave more often than others but again from the outside that's a difference in frequency and nothing else.
Where you want to go
Do you want to stay in that managerial role? Go even higher up? Maybe rather specialize on something that's unique in the company? Switch to something with lesser deadline pressure? Start consulting in your profession instead?
This section is not meant as advice but, to open your focus up a bit.
What you can do
I'm listing several things here. Pick the ones that you expect to work best in your situation and your company.
be open about it
Talk to your superiors about your condition and what it could mean. Explain that you are perfectly capable of doing your job (they should already know) and that you just may need someone to jump in for a few days, or something else that covers your downtime. That you will make an effort to make taking over where you left off easy, but don't want to push through a pain streak for the reasons you mentioned.
Risk: the company might of course view you as unfit for your role. Being open is something you have to do very carefully.
work with your team
Talk to your team about it. Get them on the same page as you are and maybe you can get them to take over some of your tasks when you're out.
Risk: this comes down to loyalty. How loyal is your team to you? But it can also build loyalty. A team lead that shows they rely on and trust the team, have the team's back and ask team to have theirs, can build the strongest team ever.
find out and point out the true size of the problem
Like I said in the beginning, while your condition is chronic your down times might effectively not be worse than those of others getting sick randomly. If that's the case use this information as a defense if somebody pressures you.
Risk: waiting until somebody puts you on the spot for a chronic disease can be viewed as keeping something from the company that affects your ability to work for them.
How would I know?
I'm currently in a turned around version of your situation. I have to go get treatments regularly where I'm completely out of order and they're planned in advance. But I get deadlines that are random, urgent and on very short notice. And the ones setting the deadlines don't care about my schedule at all.
I got my manager on my side, explaining the situation; got support from my team that for when I'm down they would cover anything that comes up as best they can and what they can't cover, they try to keep calm; and I have some bits and pieces of info on people getting sick and how that affects a company, that show that my situation is no worse than that of others, just in case anybody tried to kick me out (which hasn't happened yet, because the support I get is just awesome).