I did one of those, ended up with an opp at the nether regions, could not sit on the provided pillows (buttocks) for three months. No fun.
Mine not from slipping, but from cycling too much.
Whatever you do, don't damage that final segment of the coccyx, take my advice.
And then you ask why kids are not allowed here, radioron had to lookup the word coccyx, what would a poor grade 8 pupil think.
There is enough evidence as to keep forums PG18, not that we mind, we're adults, and know what we say, and how we say it, I hope.
We all 'sheet' from time to time, better keep the kids out of that, till they are adults and understand the full meaning.
If you have to use it a lot, and sometimes do so in front of little ones, rather use an unobtainable translation, such as kak (afrikaans), that way you don't spoil their minds, or teach them adult stuff prematurely.
And again, DO NOT CRACK THAT COCCYX SEGMENT