It really does make me so mad when employers stick so rigidly to their rule books as far as sick leave is concerned!! As if we are able to control the amount or length of time we're gonna be unwell for!... but at least your boss has been gracious enough to extend your written warning, I guess we are destined to be 'grateful for small mercies' touch our forelock as we humbly say our thank-you ma'ams.
I personally have not had any problems with insomnia, in fact, I'm normally quite the other end of the spectrum, I can sleep for England lol. Though I do know quite a lot peeps post here saying they get very little sleep, so you most definitely aren't alone on that score.
Maybe some fellow insomniacs along with your self should get together in the chat room. (Don't know just how many are aware, or have even noticed the chat room link at the top of the home page)
Hope your current flare settles down soon hun, perhaps it already is settling if there was nothing in your 'bloods'
Hugs for now