Is that right.
It was a real shock to me. Intuitively (which is to say I haven't boned up on any medical evidence) it seems that the removal of pain results in the numbing of so many nerve endings, joints, capillarys and muscles that when the drugs wear off, all of them come back to life in a mass of aches, thumping pain and shivering that I confused with my original flu symptoms and so kept medicating.
On another more risky side, despite being Christmas, I've lost over half a stone through lack of appetite induced by the same drugs, very easy to see why celebs and the like will self medicate and become addicted.