Coccyx

According to Wikipedia

The coccyx (pronounced kok-siks) (Latin: os coccygis), commonly referred to as the tailbone, is the final segment of the human vertebral column. Comprising three to five separate or fused vertebrae (the coccygeal vertebrae) below the sacrum, it is attached to the sacrum by a fibrocartilaginous joint, which permits limited movement between the sacrum and the coccyx. The term coccyx comes originally from the Greek language and means "cuckoo," referring to the shape of a cuckoo's beak[1].

There are 1,500,000 references to it on Google and most of them concern pain management and the purchasing of special cushions for people who have bruised or broken theirs.

None of which fills me with any great joy as I hurt mine last Thursday night, tumbling down the last few stairs at home when my sock-clad foot failed to make sufficient purchase on the stair carpet.

I dont think it is broken but it hurts a lot - walking about is okay, it mainly hurts as I get up and down from a sitting position or when I am sitting on a hard chair - like I was for most of today.

I sure hope it goes away soon because it is really quite debilitating, especially when the pain wakes me in the night when I turn over in my sleep.

Anyway, now you know why I keep wincing!