Chronic illness - work through flare ups or take time off

I’ve got a few chronic health issues which have been fairly calm until recently. I’m at a bit of a pinch point now where the project I’m on is crazy busy, close to an urgent major deadline and my health issues have flared up quite badly over the past few weeks.

I’m usually fine for a few hours a day but can’t really achieve much in a day, maybe 30-40% of what I usually do. I don’t have a real team or anyone to delegate to and there is a lot riding on me so I have just re prioritised to try to do just the most urgent things to prevent me taking time off and nothing at all getting done. But now I’m online and people see I’m doing stuff the work keeps piling up and I have very little energy to push back on things properly so I just keep losing track of all these emails and random requests.

The flare ups are getting worse too. I always feel well for a few hours in the morning so it feels wrong to take sick days but later i realise im not functioning and hit a complete wall

Would you take time off in my situation? I know very little would get done while im off so i feel bad but this pattern is unsustainable