I'm glad that your just sore. The important thing is that you didn't hurt your Back.
Note for all. From experience I know what makes stairs slick. Any surface that is painted will be slicker than a surface that isn't. Almost all brick or slate walks and steps are slick when wet. For those who get mail delivered to their front door, and who live in the north, might notice their carrier walking on anything but the sidewalk during and after a snowfall. There is a reason. Going up and down stairs, one should use a handrail if available, even if you've gone up and down a million times. The more times you've done it, the easier it is to slip. Going down you of course find the padding on the butt area, but doing up, you'll find the fat on your chin is much less. But if you trip going down, chins, shins, wrists and elbows can get some really bad scrapes. I can attest that sliding down stairs on your butt is the best of all worlds.