Oh yes indeed I am familiar with this. Many years ago I went sleigh riding at night and hit a very large pile of rocks. Not only did it knock me out cold but when I came to I was horrified to realize I had wet myself extensively. Being young, it was embarrassing so I never told the ER doctor. Before I went to the ER I told my friends I wanted to go home to get sweatpants on. Anyway, not only did I break my hand - called a "boxer's" fracture- but my tailbone has never been the same. An MRI also discovered it. For me if I sit on a hard surface for too long or even take a long bath it will start hurting. I worked in Accounting for years and used a thick gel like cushion to sit on. It flares up every now and again but as long as I use cushioning to sit on it usually keeps it at bay. It's on my "To Do" list to find out if it has increased in size. My Urologist mentioned that it may be a contributing factor to the extreme urgency I am experiencing. Anyway, maybe try the cushion to sit on. I know this helps me. All the best to you.