If you're comfortable having your FB friends see it (and are aware that for various reasons it could be shared, even accidentally, by your friends to their friends,) by all means. PTSD is a terrible thing to have (trust me-- I know!) so having it diminishing significantly is a major thing indeed. Congratulations on the fact that it's waning and on the amount of work you must have done to make it do so, since it doesn't diminish without a lot of hard work.
Never worry about "three steps forward and two steps back." Thirty steps forward and twenty back are still ten steps in the right direction.