I think what you mean is you haven't heard a slow blues song that is happy. Lots of up or medium tempo ones are. How about Stevie Ray Vaughan Pride and Joy? That counts as a real blues song for sure, BB was willing to play it with him. Not a sad lyric in it.
As for having to have lived the blues, I say definitely not. The only emotion necessary for music is love...love of music. Past that, I don't think that one need to have suffered to have made great music, be it blues or any other style.