There are two main versions. If you've got The classic which is the one I've got (aka the nasty horrible worst of the worst version) and you're more than a fortnight old and still alive then you'll know you've got it, although there are vast tracts of time when you feel almost well like most people you can be sure it will remind you of it's presence especially if you try and show off and push it a bit.
Then there is the non classic or secondary version which is on a spectrum from making you feel generally off and fatigued and sick most of the time all the way to just feeling mildly but constantly irritated. It is more common if you have a family member already with it, especially one with the classic version, but if you think you might have it, then ask for a blood test.
The classic and non classic can't overlap, that is, the non classic can't develop into the classic and (unfortunately) neither can the classic turn into the non classic.