I do have sarcoidosis but fortunately it has never really given me any trouble other than when it first appeared. No-one really knows why you get it and it's much more common among certain ethnic groups, particularly Scandinavians I think. As far as I remember it can attack various organs, particularly the heart, lungs, eyes.
With me it was discovered because I had large painful red lumps (erythema nodosum)all over my legs and was exhausted and very run down. My doctor was useless about it for ages and so during a particularly bad weekend dh took me to A&E where they instantly thought it was sarcoidosis. I had an ECG there and then which was how they discovered the heart murmur and I was then seen regularly by the chest clinic for a couple of years. They did X-rays which found lumps in my lungs but fortunately those never got any larger or caused me breathlessness. I also had my eyes checked.
I never had to have any treatment but it is treated with steroids if necessary. It can be very debilitating for some people but hardly affect others so is not necessarily a problem. When I was diagnosed I imagined all sorts of worst case scenarios but it honestly has never been a big deal for me at all.
Hope that helps.