I’d not feel bad if I have to cancel due to being sick. That’s perfectly understandable. You cannot go to sessions sick.
But I’d try to figure out what makes you sick. Or get new doctors. I have stomach problems too so I get it. But not being so sick that I would be in bed all day. My brother in the other hand was violently ill before being diagnosed with ulcerate colitis. Makes me wonder if they diagnosed you correctly. Throwing up chunks of food before it even goes down is scary.