| Zaister |
There are no rules for losing XP in the Pathfinder RPG. Characters never lose XP. You can, however, find the rules for negative levels in th Core Rulebook on page 562, under the heading "Energy Drain and Negative Levels", or here.
| Kolokotroni |
| ZZTRaider |
Once a player hits level 7, losing 10,000 XP can never cause them to lose more than one level...
My inclination as a DM would be to
a) not give the opportunity for it to come up before then, and
b) simply reduce the player's total XP, without adjusting their level.
Essentially, it'd become XP debt that they have to pay off before continuing to advance.
At high levels, it's unlikely that this would be any different, as you're less likely to have just crossed the break point between levels. At low levels, it's still very painful -- if you pulled the Fool right after hitting level 7, the rest of your party would be nearly level 8 by the time you returned to your original XP total.