I was going to suggest a skipping rope as good cardio even though you said no equipment. It's cheap, takes up no space and is great for burning fat, though I don't know how suitable that is with your medical condition (which I have to admit I know nothing about, looks like I need to google it before I finish this message). (Edit, skipping definitely not recommended unless cleared by someone with more knowledge then me, i.e. a physiotherapist or some such person.)
Sit-ups and crunches are pointless if you're trying to lose fat from your mid section as there is no such thing as spot reduction with fat loss. You lose fat from the whole body when you exercise, not just from one place, anyone who says differently is lying.
Okay, just read up on your condition and have to admit it makes it difficult to exercise, but not impossible.
I'd guess the best course of action would be to seek out someone in the medical profession, but i'm sure you know that anyway.
To burn some fat and sculpt your body a little i'd guess Yoga could be quite good for you, along with some gentle body weight exercises.
Sorry I can't be more specific but i'm not qualified to answer this properly and I don't want to give you bad, and potentially dangerous advice.
The best advice I can give is a quote "Abs are made in the kitchen, not in the gym."
I hope all goes well for you.
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The more I learn, the more I realise, the less I know!