I was cutting a new property for the 1st time today. It was pretty tall but not terrible. As I was cutting around the border I got the suprise of my life!!! I came very close to turning the mower over and hurting myself bad. At the lower side of the house, whoever did the grading created a bank between one lot and the other. I'm talking steep enough to really need a retaining wall, literally atleast 75-80 degrees. As I was mowing along the top at the edge the mower just kinda suddenly slowed down. I just let off the levers and sat there a second confused. The area was only maybe a 10-15 degree slope and I was confused as to why I had lost traction there. I hadn't bottomed out or anything. So I turned off the PTO and kinda lokked around me. Then I just lightly pushed the controls, very little movement. So I leaned over and looked at the right tire. It was slipping so I let off the right and put a little more on the left to turn up away from the edge. Right then the rear kicked sideways right off the hill. IT all happened very suddenly but I was somehow able to bail off. The mower slid on off the hill and to my amazement didn't turn over. Man I really don't know how it didn't roll... Anyways, after calming my nerves and getting the mower on off the bank onto level ground (yes somehow it caught and stuck on it) I went stomping back up to inspect the area to try to make some sense of what happened. With the high grass, I had mis-judged and was closer to the edge than I thought for starters. Also that high grass was hiding a washed out area. The front caster wheel was hanging over it causing a weight transfer to the left front, plus I think some of the deck weight was resting on the gage wheels. All that cause that little loss of traction. As the mower fish tailed, the left rear tire fell into another washed out rut causing it to tip over the bank. I guess it was just one of those multi condition situations that was hidden in the tall grass. A perfect little spot for disaster to strike! I still don't know how I managed to get off with one stick still over my lap, nor have I figured out how it didn't roll on over or how it managed to stop and stick on the side of that place! I mean it was tumbling over when I bailed off. Needless to say, I am counting my many blessings tonight as I sit here with no injuries and no damage to the Z. Yall be carefull out there. I just found out the hard way how you can get suprised like that when you least expect it.