First - don't panic. As long as you are reasonably well and not losing weight, coughing up blood or feeling breathless, you probably don't have anything serious.
If all you had was an Xray, then whatever it was would just show up as a patch on the film. It could have been anything from a small area of collapse due to infection, to a small area of scar tissue - the list is long.
Sarcoidosis presents with a whole lot of other symptoms and can be diagnosed by, amongst other things, a simple skin test. Also, sarcoidosis is a highly complex disease that can affect all systems of the body, and it is reasonably rare.
The best thing for you to do is to go and see your GP, explain that this is worrying you, and ask for a check up and re-referral to chest clinic.
I am sure there is nothing to worry about.
HTH