probability of a downswing.

[young nut]

I was just thinking about this in my head, but I'm not very good at statistics so I thought I would ask you folks.

Lets say a player is running very well in his last 15-20k hands, sustaining a winrate of about 6bb/100 (a well accepted unsustainable winrate) What are this players chances of having a downswing over his next 10-20k hands?

And I guess the reverse of this question would be someone on a downswing of say -1bb/100 for his last 10k hands. What is the probability of an upswing.

Assume that the player is a winning player with over 200k hands to back that up.

FYI: this post is not about me, as I do not have nearly 200k hands and I am not on an up or downswing.